Disorders of Sleep and Circadian Rhythms

Core Concepts

Insomnia: too much wake in the sleep system

Insomnia is difficulty initiating or maintaining sleep, or early awakening, despite adequate opportunity, with daytime consequences. Mechanistically, it is often described as hyperarousal: elevated activity in arousal systems and the stress circuitry keeps sleep pressure from winning the flip-flop. Contributing factors include stress, anxiety, caffeine and stimulant use, irregular schedules, and behaviors that condition the bed with wakefulness (lying awake frustrated). Chronic insomnia is commonly treated with cognitive behavioral therapy for insomnia (CBT-I) — stimulus control, sleep restriction, and cognitive restructuring — which addresses the behavioral conditioning directly; the goal is to rebuild the association between bed and sleep. Medication exists but is generally a short-term tool; any specifics belong in current clinical references, not a study guide.

Narcolepsy: the lost wake-stabilizer

Narcolepsy is a disorder of the wake/sleep boundary. The core symptom is excessive daytime sleepiness with sleep attacks — sudden, irresistible urges to sleep. Its hallmark is the intrusion of REM-like phenomena into waking: cataplexy (sudden loss of muscle tone triggered by strong emotion, while awake), hypnagogic hallucinations (vivid dream-like images at sleep onset), and sleep paralysis (inability to move while falling asleep or waking). The mechanism is well established for type 1 narcolepsy: the loss of orexin/hypocretin neurons in the lateral hypothalamus destabilizes the wake/sleep flip-flop, so the brain slips between states instead of committing to one. The REM intrusions make sense: without orexin's stabilizing influence, REM components leak into wake. Narcolepsy is the clearest clinical demonstration of the orexin system's role described in the previous topic.

Obstructive sleep apnea: breathing that wakes you up

Obstructive sleep apnea (OSA) is characterized by repeated episodes during sleep in which the upper airway collapses, stopping airflow (apnea) or reducing it (hypopnea) despite continued breathing effort. Each episode drops blood oxygen and ends with a brief arousal that restores breathing — fragmenting sleep hundreds of times a night, often without the person's awareness. The result is unrefreshing sleep, loud snoring, witnessed pauses in breathing, and severe daytime sleepiness. OSA is linked to cardiovascular and metabolic problems and to increased accident risk. The standard first-line treatment is positive airway pressure (CPAP), which stents the airway open; other approaches include oral appliances, positional therapy, and weight management. OSA is a key differential for "sleepy patient" presentations because it is common, underdiagnosed, and treatable.

Circadian rhythm disorders: clock–schedule misalignment

These disorders arise when the internal clock and the required schedule are misaligned. Delayed sleep-wake phase disorder (DSWPD) is a shift of the entire sleep-wake cycle later: people cannot fall asleep until very late and cannot wake for morning obligations — a common adolescent pattern. Advanced sleep-wake phase disorder is the mirror image (falling asleep and waking very early). Shift work disorder occurs when work hours fall outside the clock's active phase, producing insomnia at the wrong time and sleepiness at the wrong time. Jet lag is the transient misalignment after rapid travel across time zones. The mechanisms follow from entrainment: the clock shifts slowly (about an hour or so per day), so symptoms last until the SCN re-entrains. Standard approaches — bright light at the right circadian phase, consistent sleep scheduling, and (in clinical settings) timed melatonin — all work through the input and output pathways described earlier.

Parasomnias: behaviors during sleep

Parasomnias are undesirable physical events or experiences that occur during sleep. NREM arousal parasomnias — sleepwalking, sleep terrors, confusional arousals — arise from incomplete arousal out of deep (N3) sleep; the person appears awake but is not, and typically has no memory of the event. REM sleep behavior disorder (RBD) is the opposite problem: the muscle atonia of REM fails, so people act out their dreams, sometimes injuring themselves or bed partners; it is often associated with neurodegenerative conditions and is an important clinical red flag. Nightmares are frightening REM dreams (distinct from sleep terrors, which occur in NREM). Education about sleep safety — a clear path, locked windows, a protected sleep environment — is the standard management framing for arousal parasomnias; these descriptions are educational, not treatment instructions.

Common Confusions