Heat exhaustion

Heat exhaustion, which can lead to heatstroke, is a condition where an individual is taking in more heat than he or she can handle. A Human who suffers from heat exhaustion would experience dehydration, various delusions including hallucinations, and fatigue.

In 2152, Commander Tucker suffered from heat exhaustion while stranded with Captain Archer on the desert surface of the Torothan homeworld. 

To explain the lack of transportation while visiting the Skagaran colony planet in 2153, T'Pol and Tucker explained that their horses had perished several miles north of town from heat exhaustion. 

Symptoms of heat exhaustion
Symptoms of heat exhaustion can include:
 * Dizziness
 * Feeling faint
 * Visual hallucinations
 * Confusion
 * Dehydration
 * Nausea
 * Headache