Hyperthermia is a condition where the body temperature rises beyond normal. It happens when the body absorbs or produces more heat than it can dissipate. Heatstroke, a severe case of hyperthermia, occurs as a result of prolonged exposure to heat and humidity. Asphyxiation occurs when the supply of oxygen drops to a level where an individual cannot breathe normally. According to Kids And Cars, hyperthermia (heatstroke) or hyperthermia with asphyxiation are the most common causes of death related to unintentional trunk entrapment.