Question: Does sleep inertia (the grogginess experienced after waking-up) affect cognition and decision-making ability?
(a) hang up and go back to sleep;
(b) immediately start dictating instructions;
(c) wait at least three minutes before making any substantive decisions;
(d) or wait 10 minutes before making any decisions.
Answer: While your response depends to some extent on the emergency’s severity, research suggests that you’re probably better off waiting at least three minutes — but that there’s relatively little to gain from waiting more than 10.
One study, from Melbourne’s Victoria University, investigated the phenomenon of sleep inertia — the temporary grogginess and disorientation often experienced upon awakening.
After going to sleep at their normal bedtime, a dozen volunteers were roused from Stage 4 sleep — the deepest stage — between 12:30 a.m. and 5:15 a.m. by a 75-decibel fire alarm.
They immediately took a computer “fire chief” test designed to assess decision making ability. As a fire spreads from a forest to 10 houses, subjects must decide how to best use a truck, a helicopter and five dams that replenish the water supply. They had previously taken the test during the daytime.
The results, reported in the Journal of Sleep Research, were intriguing. For the first three minutes after waking, subjects performed at only 50% of their daytime level. Between three and six minutes, performance rose to 75%, and it reached 84% after 12 minutes — where it pretty much remained for the rest of the half-hour test.
Another study, from the University of Colorado - Boulder, reported similar results when they studied how sleep inertia affects cognition. In this study, nine healthy individuals were awakened and given a simple math test.
The researchers reported in the Journal of the American Medical Association that study participants had severe impairments within the first 3 minutes of awakening. Additionally, the study found that cognitive performance immediately on waking was worse than performance during subsequent sleep deprivation.
The study noted these results have important implications because many safety-sensitive occupations require individuals to perform immediately on awakening.
So always be aware of sleep inertia and its adverse effects on decision making. And the next time you get an overnight call, if at all possible give yourself at least three minutes to clear your head before making any judgments with irreversible consequences.
Bruck, D., and Pisani, DL. “The effects of sleep inertia on decision-making performance.” Journal of Sleep Research, Vol. 8, pages 95-103, 1999.
Wertz, AT, et al. “Effects of Sleep Inertia on Cognition.” JAMA, Vol. 295, No. 2, pages 163-164, 2006.