flatlining for sleeping????

On your edit, nope. Adding in "and not get stabbed or shot" makes it sound even *more* like he wants to die without the pain. Flatlining is entirely, unequivocally wrong here and there's nowhere this would make sense to a native speaker reading it.

In respones to your edit: it's understandable but confusing and likely to be read incorrectly. Flatlining has a very specific meaning (it means your heart stopping, not just death) so I'm not sure it has the kind of metaphorical one you want here. "Pass out" or "collapse" might be better alternatives.

As another writer, I appreciate your graciousness in receiving the advice you've gotten. I would say there's an idiom "to sleep like the dead," but otherwise it'd be to crash out, or to pass out, or something like that. So that'd be more like what you're thinking of.

No flatline is in reference to when a cardiogram’s line is flat which indicates the heart is not beating; therefore making you medically dead.

To answer your second question, no I think I would be confused. Are they a vampire or zombie that they are choosing to die temporarily? It's a confusing sentence. Here's some colorful phrases for sleeping you can consider for that sentence: sack out, hit the sack, drop off, saw logs (a reference to snoring), hit the hay, catch 40 winks, crash

Flatline specifically means asystole on a heart monitor. It has no other meaning. If someone’s heart is in asystole, they are dead. You cannot use that word to mean sleeping. It means a lack of heart rhythm and death. Your example in your edit also does not make sense. No one would read that and understand that it means sleeping.

No, it doesn't make sense. Just say sleep. Or maybe lie down? rest? black out? Simple is usually better, sleep works perfectly well in your extract.

I think you could ease people into the interpretation you want by explaining how exhausted he is, and reconstructing to say that he feels close enough to [death] flatline. I'll also note that, anyone saying "flatline means this and it could never mean what you want." It meant something to you, it captured the sense you wanted to convey and that's what language is and that's how language is used. That's why I suggest letting additional context try and bridge this gap. It's also important to note, before you set yourself on this edge of meaning. Is it just "natural" for the character to speak as such. You're thinking in the boundaries of meaning that demand people challenge and expand the scope of their own experience and in my opinion, that's a good thing and language and communication is enriched for it. Poetry, metaphor and simile require people to engage in this shared act of expression and reception of meaning. People might forget that some of the most idiomatic, commonplace turns of phrase and seemingly straightforward ways of talking about things and thinking about things are borne out of this tension.

"Flatline" is a slang term referring to death (specifically, under medical care, when a heart monitor shows that the heart is no longer beating). It's not associated with sleep, just cardiac arrest.

In your edit, that would be used the same way someone might say (for dramatic effect) “she was so exhausted, she just wanted to go to her room and be dead for 16 hours.” (My example was not as literary as yours. That’s likely why you’ve heard this hyperbolic exaggeration expressed as “flatlining,” instead as “being dead.”)

Oh no, to flatline is to die. It’s an EKG reference.

"Dead to the world" can mean asleep where as flat lined only means dead. Another literary phrase is sleep of the dead, though sleep like the dead would work better for your paragraph.

It’s pretty specific that the heart is not beating when you say flatlined.

If you use your example from your edit, I would think that either you are writing a weird sci-fi story where people die instead of sleep OR that you were trying too hard to be unique.

No. Flatlining does not mean sleep. It means death. It jeans your heart has stopped and the heart monitor is showing a flat line instead of a normal sinus rhythm.

Based on your sentence above (without other context from the story) I would infer the character was either suicidal or wanting to shoot up such a large quantity that he may unintentionally OD. I would not understand that he merely wanted a long deep sleep.

Re your edit: No. No one would read that and think the person wants to sleep well. People would think the character wants to die... unless you had already established in the narrative that the term means something else in the context of your story.

It just sounds like he wants to be killed painlessly and then revived? Writing it in comparison to death and weapons doesn't help it relate to sleep. Maybe some like "He was so tired: dead tired, flat lining." But it would still be a unique choice to say the least

Ok, so flatline means dead. We would understand your usage here, but it's just not what a native speaker would say. Its weird. We would say "pass out" or "pass the fuck out". That's what we say when we are talking about being extremely tired to the point of exhaustion. You could probably say he wanted to be "dead to the world" though. It might help to explain why we say flatline. This is not a reference to laying down like a flat line. It is actually a reference to a heart monitor showing a flat line when a patient dies. So like I said, we would probably understand what you were trying to say, but it's a way to say it that is so unnatural that it would be jarring to a native speaker.

As others have noted, no. The closest I can think to what you want to say is "All he wanted was to crash for approximately 16 hours ...".

… "Wanted to crash for 16 hours" as what I've said when I just need to check out and be alone/sleep. "Wished he could put himself into a coma for 16 hours… "??? BTW: one of your sentences starts with the word "seriously". Please add a comma after that word. That's grammatically correct, and it makes more sense when you read it. Good luck with your manuscript! Avoid "flatline"!

Oh, no, no. Flatlining is death, as in, all the machines hooked up to your heart and brain show flat lines. It isn't appropriate be used as a synonym for 'sleeping'. I see what you're trying to do there, but find a synonym for sleeping deeply. You could even say, 'to sleep like he was dead for 16 hours'...

Re. edit: no, I would absolutely not understand. Flatlining means you have no pulse. So it sounds ridiculous.

Your example in the first part of your edit could mean “he wants to be dead to the world while he sleeps for 16 hours” with no interruptions or life getting in the way, in a sarcastic tone. The rest after “not to get stabbed or shot” sounds to me has context clues like he wants to sleep for 16 hours in public in a very dangerous area. If not, all you need is “all he wants to do is flatline for 16 hours,” and a reader can understand that it means he just wants to sleep deeply uninterrupted for longer than a normal sleep period.

Outside of the literal sense, I would only use “flatlining” in the context of extreme exhaustion or sleep deprivation, bordering on involuntarily losing consciousness. “I’m flatlining” or “he’s starting to flatline”. “Flatlining” is an informal phrasal verb, conceptually similar to “crashing” or “conking out”. It’s a term I would mostly expect young people to use, especially after an extreme exertion. It is not at all interchangeable with generally falling asleep.

Here’s a rewrite, OP, based on what I think you are going for "All he wanted was to go comatose for the next 16 hours, without getting stabbed or shot. Seriously, what was up with this city and its denizens being armed to the teeth, huh? He could smell the metallic tang of their weapons a mile away”

Responding to your edit, I'm a native speaker and your edit makes sense to me. I read it as the character being very, very tired both physically and emotionally and wanting to completely shut off from everything for a time. It's a combination of metaphor and hyperbole/exaggeration, so the character wants to sleep *as if* they were dead. I haven't heard flatlining used that way before, which for me means it's not a cliche or trope but a new metaphor, and I think that is a good thing. There might be a difference in interpretation between american english and british english. I'm british and it worked for me. I think flatlining meaning 'in cardiac arrest' is more common in general use in the US, so it might not work as well in US english.

So it isn't a synonym for sleeping at all but it could work in the sentence that you wrote only because when reading it I would automatically assume you were being metaphorical.

To your edit, since it seems like a grim-dark setting, you could establish that the character or other characters use the phrase as a euphemism to mean heavy sleep, earlier. Or, drip that sentence in a more extreme sarcastic tone to make it clear. Or, make the character say it as dialog. "I want to flatline for 16 hours just so I don't get stabbed or shot."

somewhat unrelated but 16h sleep?

Flatlining is not a synonym for sleeping. Typically it's used in medical contexts to refer to when someone's heart stops.

I would definitely understand the sentence in your edit based on context clues! However, just reading the word flatline immediately makes me visualize someone dying in a hospital, so it’s a bit distracting. It ultimately pulls me out of feeling immersed in your story’s setting (which is otherwise described so well here).

Flatlining refers to a cardiogram that's strapped to people in a hospital reading a flat line rather than a wave (heartbeat) - so it specifically refers to the sound and look of that device as its strapped to someone who's heart has stopped. No, you cannot use flatline to mean asleep/sleeping, as it means dead/in the process of dying. Speficially in a medical setting and sense.

i'm a writer, and i would use "rest" in this context. you could also say "pass out", "catch some/a wink of sleep", "crash", "drop off"

No, many/most people will likely interpret as the persons heart has stopped.

In my experience, flatlining is exclusively used for dying. I would never use it for sleeping and I've never heard anyone do so. I'm not sure it would make sense, seeing as it specifically refers to the heartbeat stopping (simplification but yk). I guess you could use it in a very jokey manner, but not seriously.

I would not use it as a synonym for sleeping. it means dying. you could use it figuratively in the same way you'd use dying figuratively ("the construction outside caused our business to flatline"). but if you said "she got home for work and flatlined" - she's dead

Flatlining is a synonym for dying typically used in medical contexts, it refers to a heart monitor quite literally going flat when someone’s heart stops.  The Cyberpunk franchise also uses this term as slang for dying, and in the franchise characters will sometimes threaten to flatline each other, as in to kill them. Typically in regular conversation however it’s not often used, except in a medical context.

I have never heard flatlining used this way in my life. It's more so a term for dying, like when your heart stops beating and you flatline. Maybe someone on the planet has used it that way, but it is not common and might confuse the reader.

Not unless they're never waking up

Although it's not a currently used euphemism, you certainly could make it one! You could use flatline in that context if, say, someone who was so tired that they fell asleep instantly upon laying down. In a very lighthearted tone and not in a hospital, someone could say, "He was so tired, he basically flatlined right there on the couch."

"Pass out" or "dead to the world" are probably better phrases

For your update, you could use the words “pass out” or “crash”. You cannot use flatline - that means that the character wants to die.

You could sue it as an exaggeration? Like a character saying that they slept so soundly that they were practically flatlining.

I think what you're searching for is 'sleep like the dead' or 'dead tired.' Something someone might say to that effect; "My shift was so exhausting. I want to get home, peel off my uniform and just die until tomorrow." Or "He was so tired that he felt like he was flatlining." Even "My energy for today is flatlined," would be a comprehendible metaphor.

I think “pass out” would be a better term for what you’re trying to say in your edit

All he wanted was to crash for 16 hours. That would work. Flatlining is used for actual death, not a deep sleep. Crashing can mean sleeping HARD. You crash in your bed, dead to the world.