What causes nightmares?

by Marc Wilson / 07 August, 2017
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Nightmares are a misfire in the process of consolidating the events of the day.

I’ve had my share of odd dreams. One of my earliest involved finding a Matchbox car, the coolest one I’d ever seen, beneath a tree in a garden. And I also remember the feeling of disappointment, upon waking, that the toy car hadn’t left my slumber with me.

Though many dreams include odd content, I don’t think of them as bad dreams or nightmares. When I do have the odd bad dream, I can usually pin it down to some kind of disturbance in my waking life.

I’m not alone. More than 80% of people will have had at least one nightmare in the past year that woke them. Bad dreams, on the other hand, involve negative occurrences and feelings but without jolting us from sleep. Both fall under a broader umbrella of “disturbed dreaming”.

Five to 10% of us experience weekly nightmares, however, and apart from not being fun, they can also be a problem. Idiopathic nightmares – ones that have no obvious cause and wake sufferers with feelings of intensified terror or dread – are a parasomnia listed in psychiatric and sleep disorder diagnostic manuals. They are the most common weird thing (excluding apnoea) that can happen during sleep.

Having “no obvious cause” is a little misleading, because we do know who is more likely to experience disturbed dreaming: females from age 14, people with a psychiatric diagnosis and those under extreme stress. The question is why do we have them?

According to New York sleep specialist Ross Levin, nightmares are a misfire in a normal everyday process – the consolidation of memories that occurs during sleep. When we nod off – and specifically during rapid eye movement, or REM, sleep – the brain is churning through the data that has come in during the day and smoothing it into the right shape.

Ross Levin.

Sometimes, what we’ve experienced is stressful, unpleasant or scary, and this is when we are more likely to have disturbed dreaming. The anxiety-provoking experiences are cut and pasted into a mash-up and re-experienced to rid them of their impact. Levin calls it “fear extinction”.

When the experience being processed is particularly frightening, and especially for people with high levels of baseline anxiety, the exercise can get a bit intense; that is, the mash-up sticks rather too closely to what we’ve actually been through.

Rather than processing these disjointed scenes out of the fraught context in which they happened, it’s more like being forced to watch a nasty psychological thriller from start to finish. We wake up and the memories don’t get sorted properly. Or, at least, that’s what I take from it.

Knowing where nightmares spring from is one thing. But doing something about them is a subject for another time.

Meanwhile, a reminder: parents are invited to participate in a confidential online survey about adolescent self-injury and youth well-being, for which you will receive a movie voucher. If that sounds like you, please visit tinyurl.com/PES17L or email youth-well-being@vuw.ac.nz. I will summarise the results of this research in a future column.

This article was first published in the July 15, 2017 issue of the New Zealand Listener.

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