Have you talked to your parents about this? I know it might be hard to, but you do need to see a doctor. It's probably nothing serious, but you need to get checked out just in case!
Wow! Smart guy....this is common, are you eating before you go to bed? sometimes this can make you sleep restless. Sleep apnea is were a pereson stops breathing in their sleep during the night for a few seconds, this is usually people that are over weight or have a short neck, and they are almost always adults. Ask yourself.... do you feel tired during the day? If you feel full of energy as you should at 12, then you are just fine!!!
any answer to this one would be greatly appreciated i suffer from the same thing but i can't breath or move all i can do is open my eyes been happening for 20 years now