Heat Exhaustion No Fun

I did something really stupid today. It was a good morning, took the dogs to the groomers, went to the gym for a 90 minute workout, went to breakfast, picked up the dogs & headed home. So far, so good !!
After we got home, I decided to go out & continue gardening (if you call it that). I'm not good at that, so my rose bushes are about 7 feet tall, and everything has grown up around them, and around my blackberry bushes. Well, I had on long pants & a sweatshirt to keep from getting scratched by the thorns. I spent about 90 minutes out there trimming, and cutting down sumac trees, (with a handsaw, no less), when all of a sudden I began to feel sick to my stomach, and dizzy.
It then occurred to me that I hadn't had any water since I went out. When I went in it was all I could do to walk, my face was very red, and the sweat was dripping off my face.
I'm not sure if it was heat exhaustion or dehydration, or both !!!!!
From now on I'll watch what I do, and how long I do it for, in this heat. I keep forgetting I'm no spring chicken now (64), but hate to give up when I get going. Sure was STUPID on my part.