There are too many thoughts in my head at once. What's happening?

I'm trying to sleep but my brain just isn't letting me. My mind is literally overloaded with thoughts, jumping from one thought to the next within a second and they are barely even related. This has been happening for a few days now. I can barely fall asleep because my mind what STOP. I sleep about 3-4 hours a night yet I feel so energised and happy. My chest has also begun hurting and my actions are so much more fasted pace (but I don't know if these things have anything to do with it). It doesn't feel normal. I literally feel like so many thoughts are entering my head and I can't type them out in time. But I need to sleep because I've got an exam tomorrow and I've heard that lack of sleep can make you do worse. I just can't sleep. So can you please explain what's happening and how I can stop it. Thanks.