Lynn, I do not do well in the heat either and like you, I can get dizzy fast from the heat! I live in Texas and there's plenty of heat here!
I simply have to limit my outside times to keep from getting into trouble. I also drink plenty of cold fluids, iced tea without sugar is my choice. I use my ceiling fans to keep the air circulating so I do not have to run the air conditioner on 60 just to be comfortable! I usually keep the air conditioner lower at night and this gets my home really cool. Then, on with the fans after the sun is up so I can retain the flow of the cool air. Of course, I do not have little ones going in and out the door either which keeps the air colder.
In the upper nineties and triple digits, I leave the curtains closed on the sunny side so the sun cannot warm the rooms through the windows. I limit the baking indoors too as the oven will heat up my kitchen in a hurry!
If I do reach a point to where I am overheated, I have to sit quickly in a cool environment as I have to overcome the dizziness. I try to get cold fluids into my system as fast as possible. Then, it is off to the bath for a cool soak.
Trying to deal with temperatures which bring on ill side effects.