One of the things that's been emerging over the past five or six years in the literature is that REM sleep seems to serve an almost sort of overnight therapy benefit in terms of our emotional well-being and our mental health. And what's interesting is that REM sleep chemically, in terms of the anuric transmitters that swirl around the brain, REM sleep is perhaps the only time during the 24-hour period where a particular stress neurochemical called norepinephrine or noradrenaline is actually suppressed and it's completely shut down from the brain. And it seems to be that REM sleep is a perfect chemical environment, almost like a therapy session, where you can take emotional events from the prior day and perhaps just smooth the sharp edges off those experiences, and almost like an overnight soothing balm, as it were. - www.npr.org