Sleep Terrors | Why Do We Bolt Upright and Scream While Still Asleep?

A sleep terror, clinically referred to as pavor nocturnus, is a type of parasomnia characterized by a sudden, partial arousal from deep, non-rapid eye movement (NREM) sleep. Parasomnias are a category of sleep disorders involving undesirable physical events or experiences that occur during entry into sleep, within sleep, or during arousals from sleep. Unlike dreams or nightmares, sleep terrors originate from the deepest stage of sleep, known as N3 or slow-wave sleep. An episode typically begins with a piercing scream or cry, followed by manifestations of intense autonomic arousal: tachycardia (a rapid heart rate), tachypnea (rapid breathing), and diaphoresis (sweating). The individual appears terrified and confused, often with eyes wide open, but is unresponsive to external stimuli and cannot be easily comforted or awakened. A key diagnostic feature is the subsequent amnesia; upon full awakening either after the episode or the next morning, the person has no recollection of the event itself, only a lingering sense of fear at most. This lack of memory is a direct result of the brain state, where the neural circuits for consolidating experiences into memory (like the hippocampus and prefrontal cortex) are not fully engaged as they are in wakefulness or REM sleep.

The primary distinction between sleep terrors and nightmares lies in the sleep stage from which they arise and the resulting neurological and psychological experience. Sleep terrors are disorders of arousal from NREM (specifically, Stage N3) sleep, while nightmares are a phenomenon of REM sleep. REM sleep is characterized by vivid, narrative-style dreaming and near-complete muscle atonia (paralysis), which prevents individuals from acting out their dreams. Consequently, someone having a nightmare remains still, can be awakened easily, and will often recall the distressing dream content in detail. In contrast, sleep terrors occur when the brain attempts to transition from deep N3 sleep but gets 'stuck' between a sleep and wake state. This results in complex motor activity—like sitting up, thrashing, or even sleepwalking (somnambulism)—without the narrative content of a dream. The emotional experience is one of pure, undifferentiated terror, not a fear tied to a specific story. The individual is difficult to awaken from a sleep terror, and if they are, they remain confused and disoriented with no memory of a dream.

During a sleep terror, the brain exists in a hybrid state. Electroencephalogram (EEG) recordings show a sudden eruption of high-amplitude, slow-wave activity (delta waves) characteristic of deep sleep, mixed with high-frequency beta waves associated with wakefulness. This indicates a dissociation between different brain regions. The limbic system, particularly the amygdala which processes fear and threat, becomes highly activated. This activation triggers the brainstem to initiate a profound fight-or-flight response. However, the prefrontal cortex, the center for executive functions like rational thought, conscious awareness, and memory encoding, remains largely inactive, still in a sleep-like state. This neurological disconnect explains the core features: intense, instinctual fear and autonomic arousal without conscious perception or subsequent memory.

Sleep terrors are precipitated by factors that either deepen N3 sleep or increase the likelihood of abrupt arousals from it. Sleep deprivation is a primary trigger, as the body compensates by spending more time in restorative slow-wave sleep, increasing the window of opportunity for an episode. Other common triggers include high fever, significant emotional stress, or a disrupted sleep schedule. Certain central nervous system depressants, including alcohol, can also fragment sleep and lead to NREM parasomnias. In some individuals, other underlying sleep disorders that cause arousals, such as obstructive sleep apnea (where breathing repeatedly stops and starts) or restless legs syndrome, can provoke sleep terrors. In children, these episodes are often considered a feature of a maturing central nervous system and typically resolve spontaneously by adolescence.

Sleep terrors are most prevalent in early childhood, affecting an estimated 1-6.5% of children, typically between the ages of three and seven. In this population, they are generally considered benign and part of normal neurological development, often co-occurring with sleepwalking. Episodes tend to decrease in frequency and resolve as the child approaches puberty. Adult-onset sleep terrors are far less common, affecting less than 1% of the adult population. In adults, the condition is more frequently associated with underlying factors such as psychopathology (e.g., anxiety disorders, PTSD) or significant life stressors. Medical evaluation is warranted when the episodes are frequent, pose a risk of injury to the individual or others, lead to significant daytime sleepiness, or cause substantial distress for the family. A formal diagnosis may involve a clinical interview and, in some cases, a polysomnography (an overnight sleep study) to rule out other sleep disorders like nocturnal seizures.