On vary hot and humid days make sure to have water close by and pay close attention to how you feel, also know what your limitations are and if you get there and are out in the sun then find some place that gets you out of the sun if not completely inside.

I myself when I was younger and had Grand Mal's, there where times in which if was just the sun and the temp only went up to 80f I would be able to go outside for awhile. but if it was also so humid that I could feel it just as I was stepping out of the door it would make me feel as if I was going to have a seizure 5 to 10 seconds after being outside, so on those days I had to stay inside.

Stay hydrated, that's the most important,
Don't allow your body go through any dramatic changes; for e.g. jumping into water when the outside temperature is high [if you're already in the water & jump back in after being out of the water, in the hot air is OK] OR by taking a cold shower, ....
Also, gulping down a cool drink in hot weather,

Hydralyte ice blocks and plenty of water. Not too late at night though as you’ll have to keep getting up from your sleep to visit the toilet.

Its good to get out to get fresh air just don't over due it

Know my limitations if any