Sleep Terrors | Why Do We Bolt Upright in Fear Without Remembering a Dream?

Sleep terrors, also known as night terrors, are a type of parasomnia, which is an undesirable event or experience that occurs during sleep. Specifically, sleep terrors are classified as a disorder of arousal from non-rapid eye movement (NREM) sleep. They happen during Stage N3, the deepest phase of sleep, which typically occurs in the first third of the night. Unlike nightmares, which arise from REM (dreaming) sleep, sleep terrors are not dreams. Instead, they are a sudden, partial arousal from deep sleep. The brain is caught in a transitional state—not fully asleep, but not fully awake either. This incomplete awakening triggers a profound activation of the autonomic nervous system, leading to a fight-or-flight response. This results in the characteristic screaming, intense fear, and physiological reactions, all while the individual remains largely unconscious and unresponsive. The key distinction is that the frightening experience is a result of the abrupt arousal itself, not a narrative dream.

The symptoms of a sleep terror episode are dramatic and can be distressing for an observer. An individual will suddenly sit bolt upright in bed, often letting out a scream or cry. Their eyes are typically wide open with dilated pupils, but they are not truly "seeing" their surroundings and are unresponsive to attempts to comfort them. Physiologically, their body is in a state of high alert: a racing heart (tachycardia), rapid breathing (tachypnea), and profuse sweating are common. They may thrash around, kick, or even get out of bed, increasing the risk of injury. Episodes usually last from a few minutes up to 15 minutes, after which the person often lies back down and returns to sleep as if nothing happened. Crucially, the individual has complete amnesia of the event the next morning, having no memory of the terror or the physical actions they performed.

In children, sleep terrors are generally considered a normal, if dramatic, part of central nervous system development and are not typically linked to underlying psychological disorders. However, in adults, the onset of sleep terrors can sometimes be associated with psychological stress, anxiety, depression, or post-traumatic stress disorder (PTSD). It is not that the sleep terror is a direct symptom of the mental health condition, but rather that these conditions can disrupt sleep architecture, making a person more susceptible to disorders of arousal. Therefore, while not a direct indicator, persistent sleep terrors in adulthood warrant a closer look at potential contributing factors like stress levels and overall mental well-being.

Several factors can increase the likelihood of a sleep terror episode by promoting deeper sleep or making arousal from sleep more difficult. The most significant trigger is sleep deprivation. When the body is overly tired, it compensates with more time spent in deep N3 sleep, increasing the window of opportunity for a sleep terror to occur. Other common triggers include a high fever, physical or emotional stress, a disruptive sleep schedule (like jet lag), noise or light in the sleeping environment, and certain medications that affect the central nervous system, such as some sedatives or antidepressants. A full bladder during deep sleep can also act as a physiological stressor that prompts a partial arousal.

The distinction between sleep terrors and nightmares is critical, as they arise from different sleep stages and have different characteristics. Sleep terrors occur during NREM Stage N3 sleep, usually within the first 1-3 hours after falling asleep. They involve intense autonomic arousal (screaming, sweating, racing heart) with no memory of the event. The person is confused, difficult to awaken, and unresponsive. In contrast, nightmares are frightening dreams that occur during REM sleep, typically in the latter half of the night. A person having a nightmare will often wake up fully, can vividly recall the detailed and disturbing dream content, and is immediately alert and aware of their surroundings. While nightmares are a product of the mind's narrative content during REM, sleep terrors are a purely physiological arousal event from deep sleep.