The human sleep-wake cycle causes a drop in alertness between about 2 and 5 pm in the afternoon and more dramatically in the early morning between 2 and 5 am.
The afternoon slump is a natural effect of our circadian rhythms, and occurs even if you’ve had a good night’s sleep, causing reduced alertness. When sleep deprived its effect is more marked.
Workplace accidents and errors peak at the same times that our circadian rhythms cause a drop in alertness. Sleep deprivation increases this risk even more.
A power nap can improve your mood and productivity, alleviate tiredness, increase alertness and reduce errors made at work. A nap as brief as 10 minutes will produce these results. In practice this means lying down for about 20 minutes to allow time to drift off.
Napping can also benefit memory. Dr Sara Mednick’s work shows that the 20 minute nap boosts muscle memory, the 60 minute nap improves verbal memory, helping us to remember information we hear, and the 90 minute nap benefits creative problem solving.
A mid afternoon power nap has been shown to be more recuperative than a nap taken at other times of the day. If you nap at other times you will still get some benefit but it won’t necessarily prevent the afternoon slump, which is programmed in to our natural biological rhythm.
Limiting a power nap to no more than 30 minutes helps prevent grogginess (‘sleep inertia’) afterwards – important if you have to resume work following a nap. Even after a short nap it’s advisable to allow a little time before engaging in any safety-critical tasks.
If you take the opportunity to nap, but don’t fall asleep, you can still experience an improvement in mood.
References: Lovato, N., Lack, L. The effects of napping on cognitive functioning. Progress in Brain Research, Ch 9 in Human Sleep and Cognition. vol.185 pp 155 -166.