More than 70 types of sleep disorders exist. The most common problems are insomnia (difficulty falling or staying asleep), obstructive sleep apnea (disordered breathing that causes multiple awakenings), various movement syndromes (unpleasant sensations that prompt night fidgeting), and narcolepsy (extreme sleepiness or falling asleep suddenly during the day). Type of sleep disorder, prevalence, and impact vary by psychiatric diagnosis. But the overlap between sleep disorders and various psychiatric problems is so great that researchers have long suspected both types of problems may have common biological roots. Depression. Studies using different methods and populations estimate that 65% to 90% of adult patients with major depression, and about 90% of children with…