Sleep requirements vary according to your age. The need for sleep usually diminished as you grow older. Biological predisposition involves and imbalance between the two brain systems that govern sleep, the arousal system and the sleep system. The arousal system must be depressed to allow sleep. Insomniacs usually have an overactive arousal system.
Medical problems can also cause sleeplessness.
They can lead to shallow, fragmented sleep and frequent wakening. Bad sleep habits can also cause problems. If you are also on steroids, this will also cause you to be more alert and less inclined to fall asleep. Negative conditioning, like fear of insomnia, worry and depression will also cause problems. You need sleep to rest and recuperate.