Thank you for posting.
Some people cannot physically tolerate the heat, just as some people cannot tolerate the cold. A person's weight, health, and certain medications can be factors. Sometimes there is no reason at all. Some people just feel better in certain climates than in others. Talk to your PCP (primary care physician). He or she will advise you from there.
Try to stay indoors with airconditioning as much as possible in hot/humid weather. Drink plenty of water to avoid dehydration. If you are overweight, shedding excess pounds can help. You can ask your doctor for a weight loss plan if this is the case.