Seven categories of sleep disorders are identified in the International Classification of Sleep Disorders, produced by AASM in conjunction with several other authoritative sleep groups worldwide. Sleep disorders fall into these groups: Insomnia. The most common sleep disorder, insomnia falls into two major categories: trouble falling asleep and difficulty maintaining sleep through the night. Sleep-related breathing disorders. Obstructive sleep apnea is a major example. Apnea is a period when someone stops breathing. During apnea episodes, throat muscles that normally hold the airway open during sleep fail to do so, causing the airway to collapse. These episodes can occur hundreds of times in the night. Central disorders of hypersomnolence. Narcolepsy is the most familiar example of this group of disorders marked by excessive sleepiness. With narcolepsy, people have trouble staying awake and alert during the day, which affects their ability to function at work or school and can make driving dangerous. Circadian rhythm sleep-wake disorders. Conditions that temporarily or routinely go against the body's normal biological clock of being active during the day and sleeping at night, or differing from accustomed sleep patterns, include jet lag and shift work sleep disorders. Parasomnias. Unusual nighttime behavior is the hallmark of a parasomnia. Sleepwalking, night terrors, sleep paralysis and REM sleep behavior disorder are common examples. Sleep-related movement disorders. Restless legs syndrome is among the conditions involving repetitive movements that affect sleep. "A classic example is a woman sitting on a couch watching TV with her husband," Bhola says. "He's sitting quietly, whereas she has to get up and walk in circles around the couch – her restless legs are bothering her so much that she has to move or stretch them." At bedtime, a relentless need for activity and uncomfortable leg sensations can prevent you from falling asleep. Other sleep disorders. Some sleep-related conditions don't fit into the categories above. One example is sundowning – when people with dementia become more confused in the evening, often leading to sleep disruption.