REM sleep occupies about 25% of sleep time in AYAs and is characterized by a high autonomic arousal state including increased cardiovascular and respiratory activity, very low voluntary muscle tone, and rapid synchronous nonpatterned eye movements. The EEG pattern shows a low-voltage variable frequency resembling the awake state. Most dreams occur during REM sleep.

NREM sleep occupies 70% to 80% of sleep time in AYAs and is divided into three stages:

Excessive daytime sleepiness is common among AYAs. In a recent report of the American College Health Association (2013), 17.5% of college undergraduates endorsed that daytime sleepiness is a big or very big problem.⁷ In the same publication, it was noted that 10.8% of undergraduate college students reported that they had no days in the past week where they had enough sleep to feel rested, and a further 30.4% that they only had enough sleep in 1 to 2 days of the past week. Although excessive daytime sleepiness may be caused by any factor that disrupts sleep (e.g., obstructive sleep apnea) or can be a symptom of narcolepsy, the most common cause of excessive daytime sleepiness is related to insufficient sleep (“inadequate sleep”). Inadequate sleep may be due to poor sleeping habits or late bedtimes. Demanding schedules that include academic, employment, and extracurricular activities, combined with circadian delays and early weekday wake times, can leave insufficient time for sleep. Electronic devices and social media, commonly used by AYAs, may further disrupt sleep during the night.⁸ Additionally, young adults who are parents face additional sleep disruption associated with caring for young children who may themselves have difficulty sleeping.⁹ This chronic sleep deprivation can cause complaints of fatigue or difficulty staying awake during school or work, adversely affecting performance. Mood, physical health, and safety may be compromised, with drowsy driving presenting a notable risk to the 16- to 25-year-old driver.¹⁰ There are a wide variety of medications prescribed for AYAs (both for mental or physical health disorders) that can interfere with sleep, leading to insomnia or excessive daytime sleepiness. Compensatory behaviors, such as stimulant use, napping, sleeping in on weekends, poor food choices (e.g., excessive caffeinated foods or beverages), and reductions in activity, can be iatro genic, maintaining inadequate sleep and precipitating other sleep disturbances (e.g., insomnia, phase delays, SDB/apnea).

Insomnia is characterized by dissatisfaction about sleep quality or duration. Subjective complaints include difficulty falling asleep at bedtime, waking up at night and having difficulty going back to sleep, waking up too early in the morning with an inability to return to sleep, or a complaint of nonrestorative sleep. The nocturnal difficulties lead to daytime symptoms including fatigue, decreased energy and/or problems with cognitive functions and mood disturbance.¹¹,¹²,¹³ AYAs most typically have insomnia that manifests as difficulties initiating sleep at bedtime or returning to sleep during the night following a typical period of arousal. Mechanisms underlying insomnia include maladaptive sleep-related cognitions (e.g., concerns about the effects of not getting enough sleep, doubt about one’s own ability to change sleep patterns) and behaviors (e.g., leaving inadequate time to relax and unwind before attempting to initiate sleep; use of technology before bed; using the bed and bedroom for activities other than sleep, thereby reducing the association between sleep and bed). Stress, anxiety, mood disorders, and substance abuse may all be bidirectionally associated with insomnia, and a growing body of literature suggests that insomnia predicts the development of psychological disorders over time.¹⁴ Other less common causes of insomnia include physical illnesses associated with pain or discomfort, increased time in bed, or significant disruptions to sleep and daytime routines. Medications, such as selective serotonin reuptake inhibitors, stimulants, sympathomimetics, and corticosteroids, may also precipitate or perpetuate symptoms of insomnia.

A delayed sleep phase syndrome (DSPS) is a circadian phase disorder in which the timing of sleep is delayed. AYAs are particularly prone to this problem because of their busy evening schedules and an intrinsic biological preference for a later bedtime. When allowed to sleep for a normal length of time (e.g., weekends, vacations), the delayed sleep onset time will result in delayed waking time. Upon awakening, the individual will be refreshed. However, given the demands of early school and work start times, most individuals with DSPS will not be able to achieve sufficient sleep. They will have difficulty arising, experience daytime sleepiness, and be at risk of the myriad negative outcomes associated with inadequate sleep. When asked to fall asleep at a normal bedtime, well before physiologically ready, they will be at increased risk of engaging the maladaptive cognitions and behaviors associated with insomnia (described above). Difficulties with academic and occupational functioning, conflict with parents or significant others, and compensatory behaviors may further increase risk of developing a comorbid insomnia or other disorder. Based in part on normative data, Auger and Crowley¹⁵ have proposed a weekday bedtime later than 12 a.m. as a potential indicator of DSPS in adolescents over age 14 years. Using a similar approach, Robillard et al.¹⁶ have used a 1:30 a.m. or later sleep onset time and a 10:00 a.m. or later waking time as indicators of sleep phase delay in young adults, aged 19 to 24 years. It is important to note that these times are guidelines only.

The main cause of SDB is obstructive sleep apnea syndrome (OSAS). This is the presence of complete or partial obstruction of the upper airway during sleep and is associated with the following history: frequent snoring (>3 nights/week), labored breathing during sleep, gasps/snorting noises, observer episodes of apnea, daytime sleepiness, and/or daytime neurobehavioral abnormalities plus others.¹⁷ SDB/OSAS, either alone or in combination with other sleep disturbances, places AYAs at significant risk of inadequate sleep and its negative correlates including, but not limited to, excessive daytime sleepiness.¹⁸