Was I dehydrated or was it something else?

It started at football camp, we were doing some strength and speed drills and I was going at 100 percent effort we got done and I randomly felt very tired. I was constantly yawning. Then I realized I was walking like I was drunk. Before I knew what was going on I could barely see 5 feet in front of me everything else dark and felt like I was gonna throw up. I thought I just dehydratedI even though I had water right before we started. So I drank another whole water bottle and dint feel any better. I then could barely stand and finally just sat down and then fell over on my side in a cold sweat breathing heavily all of a sudden. I tried sitting up but just fell over again. One of the coaches ran over because everyone was staring at me. I told them that I was Relay dehydrated and couldn't sit or stand up. He told me just to relax until I felt better and gradually sat up without feeling as bad after about 15-20 mins then in another 10 mins I finally could stand feeling fine. But everybody thought I was faking so I dint have to do anymore drills saying that they saw me drink water right before so I was fine. But I wasn't ok something was defiantly wrong it was one of the most terrifying things I every experienced. What happened?