Because your not tired
It depends. Is this on a regulat basis? If it is so, just take some mediaction that you can directly get from the pharmacy, they'll help you sleep. If they don't work, go see a doctor.
If it's only tonight, drink green tea, or herb tea. Try listening to some music, or to the radio. Maybe you're nervous about something? Try counting endlessly.
You or thinking about something that happend in the past. Or not comfortable in side your bed.what do you do when you can't sleep?