Heat exhaustion

[Zipporah Schumaker]

a condition in which you feel very weak and sick after being in a very hot place for too long

[Zipporah Schumaker]

Heat exhaustion is excessive loss of salts (electrolytes) and fluids due to heat, leading to decreased blood volume that causes many symptoms, sometimes including fainting or collapse.
(See also Overview of Heat Disorders.)
Heat exhaustion is one of several types of heat disorders.
Heat exhaustion is more severe than heat cramps. Fluids and salts are more depleted, and symptoms are more severe. Heat exhaustion may progress to heatstroke if people continue to be exposed to excessive heat.