Not getting enough sleep can kill your mood the morning after, Norwegian researchers report.
"Not in the sense that we have more negative feelings, like being down or depressed," said lead author Ingvild Saksvik-Lehouillier of the Norwegian University of Science and Technology in Trondheim. "But participants in our study experienced a flattening of emotions when they slept less than normal. They felt less joy, enthusiasm, attention and fulfillment."
For the study, 59 volunteers spent seven nights in their own beds and slept as long as they usually do. Next, they slept two hours less than normal for three nights.
On several mornings, participants were shown more than 300 pictures on a computer screen over 14 minutes. They were asked to tap the space bar whenever an image did not contain an "X" -- a test of accuracy and responsiveness.
The reaction time was faster after the participants had been sleep deprived, "but the error rate went up," said Saksvik-Lehouillier, an associate professor of psychology. "It seems that we react more quickly to compensate for lower concentration. Then there'll be more mistakes."
The takeaway: It may be smart to avoid activities that require a high level of accuracy after a night of short sleep.
Other research has found that sleep deprivation may have the same effect on driving, for instance, as alcohol does.
Participants did better and better each day they took the test after sleeping normally but scored worse each day after less sleep, the study found.
The study volunteers also answered questions about their emotions -- both positive and negative.
The researchers didn't find clear differences when it came to negative emotions, but positive feelings scored worse after just one night of reduced sleep and dropped even more after three nights.
"We already know that fewer positive emotions have a major impact on mental health. We also know that poor sleep is included in virtually all mental health diagnoses," Saksvik-Lehouillier said in a university news release.
But not everyone needs to sleep seven or eight hours a night, she said.
"The most important thing is how you feel," Saksvik-Lehouillier said. "If you're in a good mood and alert when you get up, those are indications that your sleep habits are working for you."
The findings were published recently in the journal Sleep.
For more on getting a good night's sleep, head to the Sleep Foundation.