Insomnia
Insomnia is characterized by an inability to initiate or maintain sleep. It can also present as early morning awakening where a person awakens several hours early and is unable to go back to sleep. Difficulty initiating or maintaining sleep may often present itself as excessive daytime sleepiness, which commonly results in functional impairment throughout the day. Before being diagnosed with primary insomnia, other potential causes need to be ruled out, such as other sleep disorders, side effects of medications, substance abuse, depression, or other previously undetected illness. Chronic psychophysiological insomnia (or "learned" or "conditioned" insomnia) may result from a stressor combined with fear of being unable to sleep. People affected with this condition may sleep better when not in their own beds.