Sorry to hear. :( Sounds like he is doing better. Definitely keep him indoors the next few days drinking plenty of water.
I am an outdoors person and it gets very hot and is very humid in this part of Texas. You have to stay hydrated to have a chance outside.
If he has plans to work outside, make him plan a few days ahead to start hydrating. After the fact is too late which sounds like what may have happened today.
Stay safe in the heat.
