Why trauma replays at night

If you have lived through something frightening, you may know this pattern. The day is manageable, and then the night brings it back. Sometimes it is the event itself, scene by scene. Sometimes it is something stranger that carries the same fear. Either way, you wake with your body acting as if it is happening now.

If reading about this is hard today, it is fine to stop and come back another time. And if you are in danger or thinking about harming yourself, please call your local emergency number or reach a crisis line now.

Not a side effect, but a core symptom

Nightmares are one of the defining symptoms of post-traumatic stress disorder (PTSD). In 1989, a group of researchers went as far as proposing that disturbed sleep, and REM sleep in particular, is the “hallmark” of PTSD. Revisiting that idea in 2013, sleep researcher Anne Germain concluded that the sleep laboratory picture is more mixed than once thought, but that the clinical case is stronger: sleep problems after trauma are linked to how people fare, and treating them may speed recovery.^[1]

A review of dreaming in PTSD found that trauma-related nightmares are reported by up to 70 per cent of people with the condition.^[2]

Replays and variations

Researchers sometimes sort trauma nightmares into two kinds. Replicative nightmares replay the event more or less as it happened. Non-replicative ones change the setting, the people or the plot, but are recognisably about the same danger. The same review estimated that about half of post-traumatic dreams are exact replications of the event, which means the other half are not. Its authors added that research on the non-replicative kind, and on how dream content changes over time, is still preliminary.^[2]

A small study of 40 Australian veterans with PTSD looked more closely. Their trauma dreams ranged from replay to non-replay to a mix of both, but the emotion was largely the same across all of them: the feeling they had at the time of the trauma. The type of dream was not linked to how severe someone’s PTSD was, or to how distressing they found their nightmares.^[3] In other words, a nightmare does not have to be an exact recording to be a trauma nightmare. What often carries over is the feeling.

Why the night keeps returning to it

Nobody fully knows yet. One well-known idea comes from Ross Levin and Tore Nielsen, who in 2007 proposed a model of how dreaming handles emotion. In their account, ordinary dreaming helps take the charge out of frightening memories by weaving pieces of them into new, less threatening contexts. Nightmares happen when that process is overwhelmed, and how often and how badly depends on the emotional load a person is carrying and on how strongly they tend to react with distress.^[4]

After trauma, that load can be enormous. On this view, a nightmare that keeps replaying the event may be a sign that the memory has not yet been able to settle. It is not a sign of weakness.

A body on guard, and broken dreaming sleep

Trauma also changes the sleeping body. In the laboratory, a pooled analysis of sleep studies found more light sleep, less deep sleep and more intense eye movement during REM sleep in people with PTSD, though the differences were modest. Germain also describes evidence that heightened activity in noradrenaline, part of the body’s alarm system, may disrupt REM sleep in PTSD.^[1]

Timing may matter too. In a 2002 study, 21 people who had been injured had their sleep recorded within a month of the injury. Those who went on to develop PTSD symptoms had more fragmented REM sleep: shorter stretches of REM before it switched to another stage, and more separate REM periods.^[5] It was a small study, and it shows a link rather than a cause, but it fits a wider pattern in which broken dreaming sleep soon after trauma is associated with a higher risk of PTSD developing and lasting.^[1]

Trauma nightmares are also not confined to REM sleep. They have been recorded across the sleep cycle, and the review found that changes in REM sleep alone cannot explain them.^[2]

These nightmares are treatable

This is the part that matters most. Trauma nightmares can feel permanent, but they respond to treatment, and it can be brief.

In a randomised trial published in JAMA in 2001, 168 women in New Mexico, nearly all survivors of sexual assault and most with moderate to severe PTSD, were assigned either to three sessions of imagery rehearsal therapy or to a waiting list. Those who had imagery rehearsal had fewer nights with nightmares, slept better and had fewer PTSD symptoms at follow-up; the waiting-list group changed little.^[6] The trial had limits. The comparison was no extra treatment rather than another therapy, about a third of participants did not complete follow-up, and most outcomes were self-reported. But its starting point was that nightmares in PTSD were not usually treated directly, and its result suggested they could be.

Today the American Academy of Sleep Medicine recommends imagery rehearsal for nightmares linked to PTSD. It lists other options that may be used, including cognitive behavioural therapy, cognitive behavioural therapy for insomnia, EMDR, and exposure, relaxation and rescripting therapy, as well as several medicines.^[7] Treating sleep may help more than the nights: Germain notes that improving sleep may ease daytime PTSD symptoms and help other trauma therapies work better.^[1]

What helps

• Look for trauma-informed care. A therapist trained in trauma-focused treatment can help you work with the nightmares at a pace that feels safe. Your doctor can help you find one.
• Don’t rewrite a trauma nightmare alone. Imagery rehearsal is simple, but with trauma it is wise to do it with support, and to begin with a milder dream. Here is how the method works.
• Have a plan for waking. Name where you are, put your feet on the floor, breathe out slowly, and keep the light low and warm.
• Ask about medicines with your doctor. Some are used for trauma-related nightmares; whether any is right for you is for your doctor or pharmacist to advise.

If the nights are bringing thoughts of not wanting to be here, please tell someone today. Call your local emergency number or reach a crisis line. We have also written about why nightmares and suicidal thoughts deserve to be taken seriously.

Baku’s Nightlight, ember on black with a slow breathing pulse, is there for the minutes after you wake. It is free, and it is a companion to care, not a substitute for it.