By which mechanism the exposure to sun or for hot temperature can get us sick ( diarrhea, vomiting, high body temp.), what is the cause ?

Heat stroke: Heat stroke from prolonged exposure to high temperatures usually in combination with dehydration, leads to failure of body's temperature control system, core body temperature greater than 105 degrees f, headache, dizziness and light-headedness, seizures, confusion, disorientation, and sometimes loss of consciousness or coma, lack of sweating despite heat, red hot skin, rapid heart, nausea, vomting etc.