Headache, nausea and fatigue?

It started about three days ago when I was playing basketball with some guys. It wasn't that hot (maybe 80 degrees). But I do live in Dallas and it heats up pretty quick. But it was only 7:30am and we played until 8:30am. So after the first 30mins I was fine, but then we moved to the other side of the court in the the direct sun, and I quickly started feeling bad. I felt suddenly weak. Then went home and drank a protein shake and some water and I felt a little better, then after an hour or so, I began to feel worst. I felt nausea, got a headache and felt very weak. I also lost my appetite. The second day I began to feel bloated and no appetite as well. I ate and felt nausea. The funny thing is a young man I know said he felt the same way last week. Then after I started feeling that way, my wife started feeling the same. I don't know if it's heat exhaustion or a stomach virus. Someone please give some insight. Thanks.