Please help me with a recent health scare?

I was at a theme park over the weekend and after climbing a steep set of stairs followed by a steep hill, I realized that I was dangerously close to passing out. My breathing wasn't very labored (I am slightly overweight however) but my eye sight blurred and everything was brighter, I felt a heavy weight in my stomach, I felt light-headed and I had to sit down. There was a slight ringing in my ears, but I could hear clearly. I was a little disoriented, but I was able to calmly answer questions for the people trying to help me. When I stood up about 3 minutes later, it took me half a minute to get light-headed again and I had to sit back down. It took less than 10 minutes to completely subside, but it was a very scary moment. It was hot, but I was sweating much more profusely after the "episode". I was able to leave the park and drive home successfully, without any further symptoms. I was mostly embarrassed but now I fear that maybe it was more serious than I thought it was. I do not want this situation to occur again. Can anybody tell me what happened to me?