While heat exhaustion does not last for a specific amount of time, a doctor or other qualified health professional must be contacted if heat exhaustion lasts for more than 30 minutes, according to WebMD. Heat exhaustion can progress to a more serious condition called heat stroke after this much time has elapsed.
Heat exhaustion is likely to occur when someone is in an environment of high temperature for several days and experiences dehydration as a result. The two main types of heat exhaustion are water depletion and salt depletion. Common heat exhaustion symptoms include confusion, dizziness, fainting, fatigue, muscle cramps, nausea, pale skin, drastic perspiration and rapid heartbeat. Heat stroke is much more serious than heat exhaustion and can cause brain damage and even death, states WebMD.