Insomnia

Insomnia

is a symptom that can accompany several sleep, medical and psychiatric disorders,
characterized by persistent difficulty falling asleep and/or difficulty staying asleep.
Insomnia is typically followed by functional impairment while awake.
One definition of insomnia is
"difficulties initiating and/or maintaining sleep, or nonrestorative sleep,
associated with impairments of daytime functioning
or marked distress for more than 1 month."