Sleeping less than usual not only affects your mood the next morning but also impairs response times and other performance measures, according to research from the Norwegian University of Science and Technology (NTNU).
“Not in the sense that we have more negative feelings, like down or depressed. But participants in our study experienced a flattening of emotions when they slept less than usual. They felt less joy, enthusiasm, attention and satisfaction,” explains Associate Professor Ingvild Saksvik-Lehouillier from NTNU's Department of Psychology.
Unlike most lab-based sleep studies, Saksvik-Lehouillier and her NTNU team examined participants sleeping in their own homes. Participants first slept their usual amount for seven nights, completing cognitive tests on three mornings. They then restricted sleep by two hours for three nights, repeating the tests on two mornings.
“We all have different sleep patterns. Allowing participants to sleep at home kept their daily routines as normal as possible. During the sleep restriction phase, they went to bed two hours later than usual but woke at their normal time," Saksvik-Lehouillier notes.
Tests occurred about 90 minutes after waking, with no coffee allowed.
Participants viewed 365 images with random letters on a screen for 14 minutes. They pressed the spacebar for images without an 'x' and did nothing if an 'x' appeared.
“We measured responsiveness and accuracy. After sleep deprivation, reaction times slowed, but error rates rose. People seem to speed up to offset reduced focus, leading to more mistakes. It's wise to avoid precision-demanding tasks the morning after a short night,” Saksvik-Lehouillier advises.
Prior research equates sleep deprivation's impact on driving to alcohol impairment. After normal sleep, performance improved daily; after restricted sleep, accuracy declined progressively.
“We know sleep is crucial for learning—this may explain it," she adds.
In the second phase, a questionnaire assessed 20 positive and negative emotions.
“Negative emotions showed no clear changes, but positive ones declined significantly—after just one short night and more so after three. This is compelling, as reduced positive emotions harm mental health, and poor sleep features in nearly all mental health disorders,” Saksvik-Lehouillier states.
The study didn't track how long these effects persist, but the team plans further research on mood recovery duration.
Sleep loss is a global trend, especially among full-time workers.
“It's tempting to stay up late—'just one more episode'—yet mornings demand early rises for work, school, or family. Sleep duration matters, but so does timing. Irregular circadian rhythms can be worse than short sleep. Stick to consistent bed and wake times,” Saksvik-Lehouillier recommends.
