You’ve probably heard of insomnia, and you’re likely familiar with the concept of the paranormal. But what, exactly, is a parasomnia? Some strange combination of the two?

In a sense, yes. The prefix para-, meaning partial, and the suffix -somnia, referring to sleep, combine to accurately describe these odd disorders that manifest in the space between sleep and wakefulness. If you’ve ever had sleep paralysis, sleepwalked or experienced night terrors, you are familiar with the utterly bizarre world of parasomnias. You would probably agree that calling them a form of paranormal insomnia is not entirely wrong!

These conditions are more than a punchline, however. Parasomnia reveals interesting details about the nature of sleep and how our brains function. Moreover, we know that they can be deadly serious if they are not managed properly. Keep reading to learn what we know about this most strange set of sleep afflictions.

Caught in between worlds

In a nutshell, parasomnias refer to the unwanted physical behaviors that occur when we find ourselves in the peculiar position of being both asleep and awake at the same time. As mentioned before, sleepwalking, night terrors and sleep paralysis can all be accurately described as parasomnias; sufferers will enter a parasomniac state in the night, usually return to sleep and often have no memory of it the following morning.

During the course of a normal night, our body cycles through discrete stages, marked by slightly different brain and body functions. This is known as the sleep cycle. Though the term parasomnia encapsulates a broad category of different behaviors, all of them take place when people get “caught” in-between discrete stages of the sleep cycle and become partially awake.

What’s fascinating about parasomnia is that the specific symptoms of each of its forms arise from the unique characteristics of the two states of sleep a person gets caught in between.

NREM sleep parasomnia

Non-rapid eye movement sleep (NREM) occurs at the beginning of the sleep cycle and typically makes up about three-quarters of an adult’s total sleep time. Parasomnias that occur during this period of the cycle usually involve talking and physical movement to some degree and typically occur among younger people, aged 5 to 25. Changes to the external environment like temperature or noises can induce parasomnia during this period, as can internal changes caused by another medical condition.

Some of the most common NREM parasomnias include:

• Sleepwalking (somnambulism): Affecting between 1 to 4% of the adult population and up to a whopping 15% of children, sleepwalking occurs during the deep sleep stages of NREM (stages III and IV), typically during the earlier part of the evening. Sleepwalkers’ activities range from sitting up in bed, walking around, cooking and even driving. Sleepwalkers will have no memory of any of this activity and can react violently if they are awakened during an episode.
• Night terrors (sleep terrors): Like sleepwalking, night terrors typically occur during the deep sleep stages of NREM and soon after falling asleep. It is more common in children than in adults, for whom it affects only 1 to 2% of the population. A night terror can induce screaming, flailing, and intense sensations of fear. Sometimes sleepwalking will occur simultaneously. If a sleeper wakes up during this episode, they may become agitated and will certainly be disoriented. They typically have no memory of the episode afterward.
• Sleep-related eating disorder: This is a direct subcategory of sleepwalking whereby sufferers partially awaken from any stage of the NREM portion of the sleep cycle and subsequently begin eating or drinking in an out-of-control manner. This is most common in individuals who suffer from eating disorders while they are awake, often proving a challenging obstacle to overcome on top of existing damaging habits.
• Confusional arousal: Confusional arousal affects about 4% of the adult population according to a 2013 literature review. During an episode of confusional arousal, a person might seem to wake up, but be slow or nonsensical in their speech and thought patterns. It takes place during all stages of NREM and can occur at any point throughout the course of a night.

REM sleep parasomnias

Rapid eye movement (REM) sleep is characterized by increased brain activity and the suppression of muscle activity. During this time, vivid dreams are common; as a result, many of the parasomnias occurring during REM are linked to dream-like experiences. Like dreams, but unlike NREM parasomnia, REM episodes can often be recalled the next morning. Some of them include:

• Sleep paralysis: Sleep paralysis can occur at any time when a person enters the REM portion of the sleep cycle. It is characterized by the awareness of being awake coupled with the inability to engage any muscles in the body. It is one of the more common parasomnias, with an especially high occurrence rate among those under 30 years old. If awakened during this state, sleepers will be lucid and completely remember the episode.
• Nightmare disorder: This parasomnia involves frequent awakenings as a result of experiencing intense, vivid and unpleasant dreams. The disturbing content of nightmares is what differentiates them from dreams; they are also different from sleep terrors in that the sleeper experiencing a nightmare has the ability to recall the episode and the dream state areas of the brain are activated. Nightmare disorder refers to a clinically diagnosed condition where nightmares occur so frequently as to create a chronic disruption of sleep.
• REM sleep behavior disorder: REM sleep behavior disorder is a parasomnia whereby sleepers act out their dreams through vocalizations and physical activity. It can occur during any part of the night, but is most frequently experienced in later parts of sleep. REM sleep behavior disorder is found in about 5 to 8% of adults, though it is more common in women. Most of the time this parasomnia is marked by vocalizations alone, though physical activity can sometimes accompany it. Like nightmare disorder or sleep paralysis, sleepers can often recall the dream events they were enacting, though they may be unaware of their actions in the real world.