To keep the body healthy we need sleep. And it is the best exercise for the mind. Sleep also differ with the stress of the mind due to social or economical situations. If a problem comes to mind sleep will also be reduced. Such people go to bed not for sleep, but for thinking. Most of the reasons for lack sleep is mental problems. Rest of others are the inconvenience comes with physical diseases. Lack sleep will cause to brain diseases such as alzheimer's disease and dementia. And it also affect to reduce the memory power and reduce the power immune system.
If you do not get sleep while go to bed, do something while get sleepy. Some people do reading while they got sleepy. It is also a valuable thing. If you late to sleep normally they avoid drinking red wine, coffee or tea or chocolate. Those foods late your sleep. Drinking glass of milk or get a warm bath before one hour go to sleep is helpful for a good sleep. Do not think about the daily activities and tomorrow activities when go to bed. This will also reduce your sleep.
Psychologist Carl Rogers has said that "do not call to sleep while the sleep will call you".