Brian Fung wonders about the best thing to do when you can't fall asleep:
[Y]our best move, if you've been in bed for 20 minutes and still aren't dozing off, is to get up and engage in a low-light, low-stress activity like reading until you begin to feel tired. Taking your mind off of "Why am I not sleeping?! I need to sleep!" is crucial. When you do get up, though, don't use your computer or phone or watch TV — the blue-colored light from the screens tricks your body into thinking it's daytime and not releasing melatonin. Sweet, sweet melatonin.
All we can say is that sleeping about 7 to 8 hours is what healthy people tend to do. There’s no evidence sleeping longer is helpful, and it could be harmful.