Although there's no evidence that sleep disorders cause psychiatric disorders, the two often go hand in hand. Sleep and psychiatric disorders such as schizophrenia and depression are closely related. Psychiatric disorders are the leading cause of insomnia. And some people with psychiatric disorders have other sleep problems, including sleepiness during the day, fatigue, and nightmares. Trouble with sleep can worsen psychiatric disorders by making the person confused or frustrated, as well as more sensitive to pain and other medical problems.