I know better. I've been trained on how to stay hydrated and how to protect myself from heat exhaustion. However, on a recent load that picked up near Fort Myers, FL, I was almost overcome by the heat and lack of water in my system.
This is how it happened. I delivered in Miami, had breakfast in my truck and headed to Fort Myers to pick up my next load. I think it was about 3 hours to get to my pickup location. When I got on site, it was in the upper 90's with very high humidity as I was very near the Gulf Coast.
The load took longer than normal for me to secure because of the difficult and unusual freight. During the time of getting loaded and securing the freight, 
I should've been drinking water at the least and adding a snack with protein ideally. However, I had neither as I was so concerned about the task at hand that I didn't take proper care of myself.
After I left the shipper, I started drinking water; downed 2 bottles immediately. It was almost too late though as I started getting a painful headache and then became so nauseated that I thought I was going to throw up. I did have a Gatorade packet that I added to my 3rd water bottle and about 20 minutes after that, the nausea subsided and I was able to eat something. Soon, the headache was gone, but the whole process took about 2-3 hours. All this made for a less than pleasant drive out of south Florida.
A few days later, I found myself in the same situation- securing a difficult load in the blazing sun. This time, I was prepared and had water bottles out by the trailer with me to remind me to drink and to make it convenient as I worked.
The picture to the right is not from the day I'm referring to, but one from one of my carhauling days.