Warmer temperatures can cause discomfort and restlessness, and anyone who has slept in a stuffy bedroom can attest that it’s hard to nod off when you’re sweaty and dehydrated. A bedroom that’s too warm can interfere with your body’s thermoregulation abilities and cause
fatigue6. Often, a person who is fatigued will feel physically and mentally tired, but unable to fall asleep
Body temperature affects not only sleep onset, but also sleep quality and the time spent in different
sleep stages. A higher core body temperature has been associated with a decrease in restorative
slow-wave sleep7 and subjective sleep quality. Similarly, a bigger difference in temperature between the core and the extremities – which indicates that the body is not efficiently sending heat away from the core – has been associated with
decreased sleep efficiency8 and a higher likelihood of waking up after falling asleep.
During REM sleep, the body
ceases most temperature-regulation9 behaviors such as sweating or shivering, leaving you more sensitive to ambient temperature changes. Accordingly, excessively hot ambient temperatures also appear to lessen the time spent
in REM sleep10.
In addition to causing grogginess the next day, a decrease in REM and slow-wave sleep can negatively impact bodily recovery and the immune system, as well as learning, memory, and other processes
