Most people know that if they don't get enough sleep, they'll feel cranky and tired the next day. But according to Californian researchers, another side-effect of staying up all night is something they call short-term euphoria.
The researchers were puzzled over why some people with clinical depression say they feel more positive after a sleepless night. So they scanned the brains of 27 adults, half of whom had a good night's rest while the other half pulled an all-nighter.
The scans showed that the volunteers who hadn't slept had extra activity in part of the brain that's involved with positive feelings, motivation, sex drive, addiction, cravings and decision-making.
So while you may feel more upbeat after staying up all night - at least until the fatigue kicks in - it's not such a good idea to be overly positive if you have to make important decisions the next day, the researchers claim.
"We need to ensure that people making high-stakes decisions, from medical professionals to airline pilots to new parents, get enough sleep," says Professor Matthew Walker, the study's lead author. "Based on this evidence, I'd be concerned by an emergency room doctor who's been up for 20 hours straight making rational decisions about my health."
So make sure you don't miss out on too much sleep as the clocks go forward this weekend. And next time you're out all night, don't make any rash decisions until you've slept on them.