1. Poor Sleep Hygiene
The most likely culprit contributing to your inability to sleep is simply poor sleep hygiene. This odd phrase refers to the behaviors, habits, and choices that might make it difficult for you to sleep. If you can't sleep, it might be due to your sleep environment, an irregular sleep schedule, or other things that are ruining your sleep. Fortunately, many of these issues can be addressed once they are recognized, with significant improvements in your ability to sleep.2. Insomnia
Insomnia is simply the inability to fall or stay asleep. It also describes sleep that is unrefreshing and of poor quality. It may occur over the short-term, often as the result of an identifiable stressor, and be called acute insomnia. It also may become a more chronic condition. Insomnia can lead to great distress, and in exceptional circumstances it may be fatal (such as in fatal familial insomnia). Fortunately, there are many treatment options available.3. Restless Legs Syndrome (RLS)
For those who are afflicted with restless legs syndrome (RLS), the symptoms associated with it are easily identifiable. Most people with RLS describe an unpleasant sensation in their legs that occurs during the evening, often as they are falling asleep, and is relieved by movement. These movements may become extreme enough that you can't sleep. If associated with uncontrolled movements of the arms or legs, such as in periodic limb movement syndrome (PLMS), it might even make it difficult for your bed partner to sleep. There are many potential causes of RLS, and there are a few excellent treatment options.4. Circadian Rhythm Disorders
It is quite possible that you can't sleep because your body desires to sleep at the wrong time. This is the case in those individuals with circadian rhythm disorders. The circadian rhythm refers to the natural pattern of the body's functions, including the drives for hunger and sleep. Most people desire to sleep overnight. However, if your circadian rhythm is shifted early (as in advanced sleep phase syndrome) or late (as in delayed sleep phase syndrome) your desire to sleep will likewise shift.
For those with delayed sleep phase syndrome, this may mean that you are a night owl and it will be difficult for you to fall asleep at an earlier time. You will likely lie in bed awake for hours at the start of the night, but then have difficulty getting up in the morning. This condition may be effectively treated with melatonin, a light box (phototherapy), or even behavioral therapy.

