How to say "I can't sleep because I am thinking about something all night long" in natural English?

*This test has me stressing. I can't even sleep.* *I stayed up all night worrying about the exam.* *I was up all night tossing and turning. I'm totally stressed out!*

My mind is racing.

Changing the second part to “I have been thinking” would sound more natural. The present tense sounds like you want to stay awake. But if that is the case, “because I have to think about something all night” would sound better. It helps to know who you’re saying this to in the middle of the night and why. If someone asked why you can’t sleep, saying the whole sentence would make sense. But if you were introducing the subject of why you can’t sleep saying “I can’t sleep.” Then ending the sentence and saying “I’ve been thinking about something all night.” would sound better.

The phrase "tossing and turning" comes to mind-- "I was tossing and turning all night, worrying about my exam." It means the same as what you've said, implying that you were rolling around in bed, unable to settle down or get comfortable. I might also say something like "I was up all night worrying about my exam" or even simply just "I didn't sleep well because I was anxious about the exam." Just so you know, it should never be embarrassing to say something in a non-native language in an unusual way! Even if it sounds a little strange, I could easily understand what you meant, and that's what matters. Keep up the great work :)

I was tossing and turning all night. Maybe

"Something" kept me up all night.

I can’t sleep because my mind is racing. Weird idiom but natural.

i was tossing and turning all night thinking about the exam. I couldn’t sleep because of the exam the next day. The stupid exam had me so anxious that i could go to sleep until midnight.

couldn’t sleep, my brain decided 3am was the perfect time to remind me of every embarrassing thing i’ve ever done

i was instead of I am

“I was awake all night thinking of ___”

I was tossing and turning all night. Is a common phrase indicating a restless night.

“Couldn’t sleep last night” or “wasn’t able to sleep last night” is for sleep the night before/early morning hours of today. “Can’t sleep these days” is for a recurring issue. To exaggerate, you could claim having insomnia. “I’ve got insomnia over this exam.” I won’t be able to sleep tonight because of this exam. I won’t be able to sleep until I take this exam!

There isn't a specific phrase for it. You could say "I was up all night worrying about..." Or "I couldn't sleep last night because I couldn't stop thinking about..." Both work, both sound fine.

I tossed and turned all night worrying about my test. I couldn't sleep because my mind kept thinking of all the things I need to remember for my exam. Worrying about the test kept me up all night. Are just 3 examples

“I can’t sleep because of it” “I’m losing sleep over it”

I couldn't sleep because I couldn't turn off my brain.

I would probably say something like, "I was up all night last night worrying about the exam. I barely got any sleep at all."

X had me tossing and turning all night, I didn't sleep a wink.

My mind is racing.

one option for you - “I didn’t get any sleep - I was tossing and turning all night, I’ve had a lot on my mind”

My mind was racing all night.

Great answers so far. One other way to say it would be: I was so "worried about something" or "so preoccupied with something" that I didn't sleep a wink last night. Here's another one: I'm not getting any sleep these days. I keep thinking about "X"

____ kept me up all night. The test, my date, my appointment, etc.

I couldn't sleep last night because my brain wouldn't shut the fuck up.

I can't sleep because my mind is spinning.

Using the example you gave you could use “I was tossing and turning all night thinking about the exam”, or “I am/I was losing sleep over the exam”

There’s not much wrong with the sentences as you’ve written them. If you’re describing something that often happens, I’d rewrite the first one as “I can’t sleep because I’m thinking about things all night long”, although if you’re thinking about the same one thing every night then your sentence is better. Your second example, is only wrong in its verb tenses. You’re describing something that has happened and concluded, so it should be “I couldn’t sleep, rolling on my mattress til midnight because I had an important exam the next day”.

"Tossing and turning all night," is a common phrase.

Couldn’t sleep - night thoughts!

Something is keeping me up all night.

"my brain wouldn't turn off" or "my brain wouldn't shut up" "i couldn't get comfortable last night" "sleep did not come easily to me" "I counted sheep so long that they unionized and complained about the long hours they were putting in" ('counting sheep' is a common folk method to solve insomnia - you imagine sheep jumping over a fence one by one, and thinking about that or something similarly boring is supposed to allow your brain to relax enough to fall asleep)

I couldn't shut my brain off.

I couldn't sleep last night, because I kept thinking about the exam. I tried to take my mind off it by reading a book, but I couldn't concentrate. No matter what I did, my mind drifted back to worrying. I even began to worry about my lack of sleep, and that just exacerbated my anxiety. It became a vicious circle - I couldn't sleep because I was worrying about my lack of sleep, which prevented me from sleeping, which made me more worried... (Most people probably wouldn't say "exacerbated". I use some rather unusual words sometimes.)

I tossed and turned all night. My mind was racing because of this test that's coming up.

The thought of something kept me up.

I didn't sleep much last night because I kept worrying about my Dad. I couldn't fall asleep last night because I have so much anxiety. My insomnia is getting worse. I just lie in bed thinking about everything and I can't shut my brain off.

I can't sleep, I have something on my mind. I can't sleep, I've been thinking about an exam I have tomorrow. I've been tossing and turning on my mattress for hours, I'm thinking about this exam I have tomorrow. I tossed and turned on my mattress until it was midnight, I was thinking about an exam I have/had today.

It sounds like you're going for "I can't sleep because I *have been* thinking about something all night long," assuming you are saying this while sleeping is still a problem. You could say "I *couldn't* sleep because I *was* thinking about something all night long" if you're talking about, for example, why you didn't sleep last night.