I absolutely agree - recently it was quite a hot day. I'd helped two other riders out with their horses and than went to ride mine. I was rather tired and hadn't remembered to drink enough water. I than rode my horse, Chinga and finished. Therefore; I had ridden three horses in one morning. This resulted in me becoming dehydrated. I than "instructed" a friend of mine - offering her a few tips.
I ended up passing out, twice.