Probably the most common is Insomnia. I will also consider night terrors, Kleine Levin Syndrome, and the effects that some drugs have on REM sleeps. Insomnia, itself, is not a disease but it might be a symptom of many diseases. Insomnia is not denied by the number of hours of sleep, or how long it takes to fall asleep. Insomniacs can have some troubles during the day, such as tiredness, lack of energy, difficulty concentrating and irritability.
Insomnia is inability to sleep prematurely interrupted by periods of wakefulness.
We can classify Insomnia according to how frequently it happens. Some environmental influences might be extreme temperatures, environmental noises, changes in surrounding environment, jet lag, medication side effects, and consumption of some drugs, such as caffeine, nicotine or alcohol. As far as treatment of insomnia is concerned, transient and intermittent insomnia may not require treatment since episodes lasts only for few days at a time. Behavior that may worsen insomnia is drinking a lot of coffee. There is also possibility using some sleeping pills, but not for long time term use.