Heat makes people sleepy because of the mechanisms the body uses to keep itself cool, lack of adjustment to warm temperatures and lack of sleep due to exposure to hot, humid nights, according to Global Bioweather. The human body takes several days to acclimate to the heat, and a person who has not acclimatized to warm weather is likely to feel sluggish. Oxygen levels and blood pressure are also lower.
Global Bioweather explains that the human body prevents overheating by opening blood vessels to carry more blood to the skin. Widened blood vessels result in the lower blood pressure and reduced oxygen levels that cause heat fatigue. This fatigue often results in individuals becoming moody, aggressive and displaying slowed reaction times.
Individuals with certain health conditions, such as obesity, high blood pressure and kidney disease are more prone to heat exhaustion, according to WebMD. Heat exhaustion is a medical emergency that occurs after exposure to heat for several days. There are two types of heat exhaustion. Water depletion heat exhaustion results in excessive thirst, weakness, headaches and loss of consciousness. Salt depletion heat exhaustion results in nausea, vomiting, muscle cramps and dizziness. Treatment for heat exhaustion includes re-hydration, using ice towels and fans, removing unnecessary clothing and taking cool showers.