A long-term pattern of difficulty sleeping. Insomnia is usually considered chronic if a person has trouble falling asleep or staying asleep at least three nights per week for three months or longer. Some people with chronic insomnia have a long-standing history of difficulty sleeping. It's the most common sleep disorder, yet often goes undiagnosed and untreated, according to a new report. The consequences can be much more serious than daytime sleepiness. Research has linked insomnia to high blood pressure, congestive heart failure, diabetes, and other ailments.