Contrary to popular belief, ‘sleeping on a problem’ could only make the matter worse.
The study by the University of Massachusetts Amherst found that negative thoughts and experiences become more upsetting if you sleep immediately afterwards rather than digesting the problem while still awake.
These findings contradict previous studies that suggest sleeping and dreaming take the edge off sad experiences and emotions.
The study involved asking 106 young participants to look at a series of upsetting pictures and then rate their emotional response. The volunteers were then shown a different set of pictures after a 12 hour gap and were asked to give fresh feedback.
They discovered that those who slept overnight between looking at both sets of photos were better at recognising the images and had retained a stronger, more negative feel towards them, compared to those who saw them once in the morning and then in the evening, without any sleep in between.
Researchers from this study decided to look at this situation from an evolutionary perspective and explained that by the brain retaining vivid, negative memories, this teaches it to avoid repeating these experiences in the future.
"We found that if you see something disturbing, let's say an accident scene, and then you have a flashback or you're asked to look at a picture of the same scene later, your emotional response is greatly reduced, that is you'll find the scene far less upsetting if you stayed awake after the original event than if you slept,” says Dr Rebecca Spencer, from the study.
Dr Spencer added that this study shows that sleep preserves our memory and our sensitivity towards them.
"Some previous studies have looked at just memory itself, not how emotional reactivity changes. When they looked at how our responsiveness changes they have a different and limited measure,” says Dr Spencer.
"There have been a few studies which look at one or the other but this is the first to look at them side by side."
Lesley McCall, a cognitive hypnotherapist, agrees that it’s not ideal to sleep straight after a stressful event.
“Taking huge amounts of stress into sleep with you is not good for you. Whilst REM (rapid eye movement) sleep is your mind's way of de-stressing itself, too much stress can increase REM sleep to the point where your slow wave sleep (where you get refreshed and relaxed) is reduced significantly.
"This means that you may wake up anxious, tired and miserable – and more likely to remember the stressful moments as soon as you wake up,” Lesley told The Huffington Post.
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