Everyone has good and bad dreams. It's like a live horror movie playing in your mind, probably waking you up right before something terrible happens.
For example, falling off a cliff or about being murder - relieved when you realize it's just a bad dream, it wasn't real.
But did you know there are actually two types of sleep conditions that fall under the "bad dream" umbrella? Nightmares and sleep terrors (also called night terrors).
This is partly due to the stage of sleep the event happens in. Nightmares occur during rapid eye movement (REM) sleep. This is the stage of sleep when vivid dreaming is most likely to happen, according to the American Sleep Association (ASA), and the brain is more active than it is during other stages of sleep.
Sleep terrors typically happen during non-REM sleep, specifically stage three sleep. This stage is also called deep sleep, where according to the ASA, extremely slow brain waves start to appear, interspersed with faster waves.
According to the National Sleep Foundation, there are a few things that increase the likelihood of having a nightmare, including eating before bed (your metabolism kicks in, keeping your brain active), medications including certain antidepressants, lack of sleep, sleep disorders like restless leg syndrome, and stress.
Recurring nightmares, or bad dreams where the same theme or events play out, are especially prevalent among trauma survivors and people with PTSD, according to the U.S. Department of Veterans Affairs.
According to the Mayo Clinic, a few things can trigger sleep terrors including sleep deprivation, stress, fevers, and changes in sleep schedule (like travel or jet lag). Sleep apnea, restless leg syndrome, and alcohol use can also increase the likelihood of sleep terrors.
Sleep terrors are more common in people with mood or anxiety disorders, including PTSD. They're also more prevalent in people who sleep walk and/or talk. This is because sleep terrors, sleep walking, and sleep talking are thought to have similar underlying mechanisms in the brain during sleep; they also tend to occur during the same stages of sleep.