Go through these in order and stop at the first one that applies. If you are reading this for someone else, answer for them.
Call emergency services if heat exposure is followed by:
These can be signs of heat stroke or another emergency.
While waiting for help, move to a cooler place, remove excess clothing, and cool the skin with water, cool cloths, or fans.
Do not give drinks to someone who is confused or unconscious.
Seek same-day medical advice if you develop dizziness, headache, nausea, marked weakness, or cramps that do not improve after about 30 minutes in a cool place with rest and fluids.
Repeated vomiting or a new inability to sweat while overheating also needs prompt assessment.
Arrange a routine appointment if heat intolerance is new, keeps returning, is getting worse, or interferes with sleep, work, exercise, or daily activities.
Also make an appointment if it comes with unexplained weight loss, persistent tremor, frequent palpitations, major changes in sweating, or new menstrual changes.
Every sign above is quoted from the sofidex article on Heat intolerance. If you are not sure, err upward — it is always reasonable to be checked.