Tropical climates knock me out.

I'm wondering if anyone else experiences this. I first noticed it when I lived in Japan 10 years ago. I was feeling exhausted all the time: very low energy, limbs like lead, sleepy. I never seemed to get enough sleep, never felt rested. A doctor ran a bunch of tests and said I was normal. When I came back to Canada, the symptoms went away and I didn't give it another thought.

Well, now I'm in Thailand, 10 years later, and the fatigue is back! Exactly the same symptoms. The climate is very similar: extremely hot and humid, with ubiquitous (and necessary) use of AC. I'm forming the conclusion that tropical climates (and possibly AC machines and mould) are unhealthy for my northern constitution.

I'd like to know if anyone else has experienced this too.

EDIT: Thanks, everyone, for all the advice. I'm drinking a gatorade now and it oddly feels more refreshing than water. I've never liked gatorade but oh man is it hitting the spot.