It sounds like you suffer from heat exhaustion, heat exposure or sunstroke.
Exhaustion symptoms or excessive fatigue disorder has three defining characteristics:
Feelings of excessive fatigue, weakness, and lack of energy,
Increasing irritability, and
Feelings of demoralization
Causes of Exhaustion:
Stress
Adrenal Insufficiency
Hypothyroidism
Anemia
It's also a possible side effect of many prescription drugs, including beta blockers, muscle relaxants, and mood stabilizers
Warning signs of heat exhaustion include:
heavy sweating
paleness
muscle cramps
tiredness
weakness
dizziness
headache
nausea or vomiting
fainting