An insomniac is someone who suffers from insomnia, a sleep disorder characterized by difficulty falling asleep or staying asleep. Insomnia can be caused by a variety of factors, including stress, anxiety, depression, and certain medications. It can also be a symptom of other medical conditions. People with insomnia often experience fatigue, irritability, and difficulty concentrating during the day. Treatment for insomnia typically involves lifestyle changes, such as avoiding caffeine and alcohol before bed, and cognitive behavioral therapy.