A sleep disorder is a condition that involves any type of difficulty that relates to sleeping. This includes difficulties falling or staying asleep, falling asleep at inappropriate times, excessive total sleep time, or abnormal behaviors associated with sleep.

More than 100 different disorders of sleeping and waking have been identified. They can be grouped in four main categories:

• Problems with falling and staying asleep
• Problems with staying awake
• Problems with adhering to a regular sleep schedule