It’s one of those days: you’re depressed and defeated the moment you open your eyes. The weight of things you should have done and all the things you need to do makes it a struggle to crawl out of bed. Or it’s the kind of day when you wake up feeling sullen and out of sorts. Anyone who crosses your path—partner, child, colleague, friend—gets the crabby treatment.
Waking up on the wrong side of the bed often has to do with being short on sleep, and in recent years scientists have begun offering theories about why this is so.
Sleep scientist Rosalind Cartwright discusses her theory in her latest book, The Twenty-Four Hour Mind: The Role of Sleep and Dreaming in Our Emotional Lives. Cartwright’s research suggests that one function of sleep is the down-regulation of negative emotion. This leveling out of emotion does not occur during quiet sleep, which takes place mostly in sleep cycles in the first half of the night. Rather, it occurs toward the end of the night during episodes of REM sleep, when you’re having dreams.
REM Sleep Deprivation
The evidence that REM sleep regulates mood comes mainly from studies where subjects have been deprived of REM sleep. Invariably, they awaken in a bad mood. Overall they’re more fearful, more easily thrown off kilter by problems that arise during the day, and less able to enjoy events that would normally bring pleasure.
So how could REM sleep deprivation lead to waking up in a bad mood? Cartwright notes that the majority of dreams with emotional content are disturbing rather than pleasurable. The function of these disturbing dreams, she claims, is to enable you to process the negative experiences you have during the daytime.
How Dreaming Works
Your waking experiences get reactivated during sleep, carried forward into REM sleep, and matched to memories of earlier experiences of a similar emotional tone. Dreaming does not lead to the forgetting of recent disturbing events but rather helps to defuse their emotional charge. You then awaken in a more positive frame of mind.
So getting a full night’s sleep helps you smooth out negative emotions and stock up on emotional reserves. If you can’t sleep your fill, whether you’ve gotten to sleep too late or awakened too early, it’s REM sleep and dreaming that often get shortchanged. And “loss of REM,” Cartwright says, “may equal direct expression of negative mood.”