A parasomnia disorder is a disruptive sleep disorder that occurs during an arousal, or phase of wakefulness, from REM or non-REM sleep. Unlike disorders that keep you from getting to sleep or staying asleep, such as insomnia, restless leg syndrome or sleep apnea, parasomnia disorders occur when you are already asleep, and may not even wake you up. However, these kinds of disorders can still contribute to a reduced quality of sleep, leaving you feeling fatigued the next day. Parasomnia disorders include nightmares, night terrors, sleepwalking, nocturnal teeth grinding, and sleep paralysis. If you have or think you have a parasomnia disorder, the good news is that you can improve many of these conditions with healthy sleep practices.

Parasomnia disorders can have psychological or physical causes. For instance, stress and anxiety or an underlying medical condition can both be causes of a parasomnia disorder such as excessive nightmares. Bad dreams are the most well-known and dreaded negative aspect of sleep, though the occasional nightmare doesn’t qualify as a parasomnia disorder. Nightmares are dreams with frightening, disturbing or upsetting content that causes the dreamer anxiety, fear or distress. People typically wake abruptly from a nightmare and can remember their dream in detail. If you’ve been having frequent nightmares, the cause might be an underlying illness, a reaction to medication, anxiety and other psychological conditions, or a recent trauma in your life such as the loss of a loved one. Luckily, there are techniques of controlled dreaming and active visualization you can use to get to the root of your nightmares and turn them into more pleasant dreams!

Night terrors are a related but more rare parasomnia disorder occurring in non-REM sleep. A person with night terrors will also wake abruptly, but may be unresponsive to questions, and will seem to be confused and in the grip of extreme terror. This disorder is typified by thrashing movements and what bystanders describe as “bloodcurdling screams”. Sufferers usually don’t remember having night terrors the next day. These nighttime frights are part of a broader category called arousal disorders, which also include confusional arousals and sleep paralysis.

Confusional arousals occur when someone wakes or is woken in the early part of the night: sufferers emerge from deep sleep with exaggerated slowness and will exhibit confusion. This kind of parasomnia disorder is also called “ excessive sleep inertia” or even “sleep drunkenness”, and like night terrors, sufferers often don’t remember a confusional episode the next day. In fact, some researchers think confusional arousals might be more likely in people who have short-term memory problems.

Then there’s sleep paralysis, which has been classified by some researchers as a disorder even though healthy people sometimes have them spontaneously or even induce them deliberately to trigger an out-of-body experience. Your brain naturally paralyzes your large muscle groups before you enter REM sleep (a condition called REM atonia), in order to prevent you from acting out your dreams. Sleep paralysis occurs when you wake up before your body has had a chance to emerge from REM atonia, meaning that your brain is awake while your body is still asleep and paralyzed. While it isn’t dangerous, sleep paralysis can be a scary experience for those who don’t know what’s happening.

More serious are physical parasomnia disorders such as sleepwalking, teeth grinding, and REM sleep behavior disorder (RSBD), which could be described as the opposite of sleep paralysis. In this rare parasomnia disorder, sufferers physically act out their dreams, which are frequently violent or action-filled. Besides carrying the potential for injury to oneself or a bed partner, in about 50% of sufferers REM sleep behavior disorder is a sign of serious neurological conditions including Parkinson’s disease, dementia, or multiple system atrophy (in which neural connections in several areas of the body begin to break down). This parasomnia disorder can also occur in reaction to certain types of sleep medication, which is why a physician’s diagnosis is crucial to understanding and treating RSBD. As with nightmares, people with RSBD can usually remember their dreams in detail upon waking.

Another active parasomnia disorder is sleepwalking. Once considered a childhood phenomenon, researchers have discovered that sleepwalking can occur at any age, though it’s most common in kids aged 8-12. Sleepwalkers usually do so in their first 3-4 hours of sleep, or in early-stage REM sleep. As the name suggests, walking around is the most common manifestation of this parasomnia disorder, but sleepwalkers may also move objects around or undress themselves. Unlike RSBD, sleepwalking doesn’t necessarily hint at a deeper neurological problem, although it can be caused by sleep medications or psychological conditions like anxiety, schizophrenia or Tourette’s syndrome. Migraine sufferers may also be prone to sleepwalking. Finally, contrary to popular belief, it probably isn’t dangerous to wake a sleepwalker: they’ll just be disoriented for a brief period before fully waking.

The last parasomnia disorder on our short list is nocturnal teeth grinding, also called bruxism from the Greek, “to gnash one’s teeth”. In this parasomnia disorder, a person clenches their jaw or grinds their teeth from side to side while asleep. Bruxism is a learned habit that can develop in response to stress, gastrointestinal or other medical ailments, or recent trauma such as a car crash. Teeth grinding can cause symptoms such as jaw or neck pain, headache, earache, ringing in the ears, insomnia, anxiety or depression, loose teeth or gum recession, and can cause tooth damage if left unchecked. However, sleep labs can identify teeth grinding in an overnight session, and usually treat it by fitting sufferers with a tooth guard or device that wakes them up when the habit begins.

We rely on our brains to initiate and maintain sleep in a complex process that can be disrupted by different physical and psychological factors. If you have trouble getting to sleep, staying asleep, or waking up, you can often improve the situation by developing healthy sleep habits and getting a physician’s advice to help you identify the problem.