Nightmares: why bad dreams wake you up

A nightmare is a frightening dream that wakes you, and that you remember. Both halves of that definition matter, because they are what separate nightmares from the other alarming things that happen at night — and those are frequently confused with each other in a way that leads people to worry about the wrong thing.

Nightmares are REM phenomena, which determines nearly everything about them. REM periods lengthen through the night and are concentrated in its second half, so nightmares cluster toward morning rather than shortly after falling asleep. They have a narrative: characters, a setting, a sequence of events, usually building toward something. You wake from one alert and oriented, aware of where you are, and able to describe what happened in detail. Getting back to sleep is often the hard part.

That profile distinguishes them sharply from night terrors, which arise from deep non-REM sleep in the first third of the night, involve dramatic outward behaviour and are typically not remembered at all — the article on night terrors in this section covers the contrast in full. It also distinguishes them from sleep paralysis, where you are awake and immobile in a real room, and from false awakenings, where you have not actually woken. If you can describe the plot, it was a nightmare.

Occasional nightmares are close to universal, and frequent distressing ones are a recognised disorder. Nearly everyone has them from time to time; they are especially common in childhood and become less frequent for most people in adulthood. A small percentage of adults have them often enough for them to matter — and the clinical distinction does not rest on the content or on some threshold of how many per month, but on impact. When nightmares cause significant distress, disrupt sleep, or create daytime consequences such as fear of going to bed, that pattern is recognised as nightmare disorder.

Several associations are well documented. Waking stress reliably increases nightmare frequency, which is covered further in this section's article on stress and dreams. Trauma is strongly associated, and post-traumatic nightmares are a recognised feature of PTSD, often replaying or echoing the traumatic event more directly than ordinary dreams do. Some medications list vivid dreams or nightmares among their effects, and withdrawal from substances that suppress REM sleep produces a rebound in REM that commonly brings intense, disturbing dreaming with it — the same mechanism described in this section's article on alcohol and caffeine. Anxiety and depression both show associations, as does disturbed or fragmented sleep from any cause.

The best-supported psychological treatment is imagery rehearsal therapy. The approach is simple to describe: while awake, the person writes out a recurring nightmare, then deliberately rewrites it with a different course or ending, and rehearses the new version mentally on a regular basis. It sounds too straightforward to work on something that feels as involuntary as a nightmare, but it has accumulated the strongest evidence base of the psychological approaches to nightmares, including in trauma-related cases. It is usually delivered by a therapist, and it is not the only approach available.

What is much less supported is the intuition that a nightmare must be interpreted before it will stop. There is no evidence that decoding the content is necessary, and treatments that work — of which imagery rehearsal is the clearest example — do not rely on it. This is worth stating on a site with a symbol dictionary: a recurring nightmare is better understood as a pattern that can be changed than as a message that must be deciphered first.

A few ordinary things help at the margins. Regular sleep timing reduces the fragmented, REM-heavy nights that nightmares favour. Alcohol close to bedtime tends to make the second half of the night worse. And winding down rather than carrying the day's rumination into bed makes a measurable difference to dream affect.

If nightmares are frequent, distressing, following a traumatic event, or affecting how you function during the day, that is worth raising with a doctor — effective treatments exist, and it is not something to simply endure.

Frequently asked

Dream symbols on this topic

• ☽ Falling dream meaning — interpretation
• ☽ Dreaming about drowning — meaning and interpretation
• ☽ Dreaming about being chased — meaning and interpretation

What this is based on

• Sleep-medicine diagnostic criteria for nightmare disorder
• Clinical research on imagery rehearsal therapy for nightmares
• Literature on nightmare associations with stress, trauma and REM rebound