Insomnia

Insomnia, also known as sleeplessness, is a sleep disorder causing difficulty falling asleep or staying asleep for as long as desired. Insomnia is typically followed by daytime sleepiness, low energy, irritability, and a depressed mood. It may result in an increased risk of accidents as well as problems focusing and learning. Insomnia can be short-term, lasting for days or weeks, or long-term, las... (Wikipedia)