We think we're tired because of the heat, but science points to a silent enemy: the destruction of REM sleep

Extreme heat drains energy not only during the day but also by degrading sleep quality at night, worsening summer fatigue.

Hot nights increase micro-awakenings and reduce REM sleep, undermining physical and mental recovery.

This ordinary heat-related tiredness is different from heat exhaustion, a medical condition that can progress to heatstroke.

Recognizing the difference matters so heat-related fatigue is not mistaken for a harmless slump.