Insomnia is a sleep disorder characterized by difficulty falling asleep, staying asleep, or both, even if you have ample time and a bedroom environment conducive to restful sleep. It can cause daytime sleepiness, a lack of energy, anxiety, depression, or irritability, and may also lead to impairments in daytime functioning, such as difficulty concentrating. Insomnia can be caused by a variety of factors, including stress, anxiety, depression, medical conditions, medications, and disruptions to circadian rhythms due to travel or shift work. Treatment options for insomnia include cognitive-behavioral therapy, sleep hygiene practices, and medications such as sleeping pills.