First of all I will say im at a loss on this because I play tennis basically everyday year round, and I also throughout the years have done alot of strength and fitness training and so I consider myself to be in excellent physical shape. But, I have what I consider to be a serious problem with my tennis concerning playing in the heat. I rarely have issues with cramping like some, but rather I will very often not feel very good or feel sick when it is very hot and/or humid out. I believe it is only heat related as well because when Im playing inside or in normal temperatures Ive really never had a problem like this as when theres alot of heat. I do sweat a ton and people that know me would say I sweat more than anyone else. I consider myself to be exceptionally strong, fast and usually more so than anyone I play, but I suffer in the heat. I often am feeling sick to my stomach, light headed, and my legs feel extremely fatigued in the quads and cavs. I will sometimes feel like im going to throw up, but I never have actually. Over the last few years Ive tried to do alot of things to help it, namely wearing all white and using sunscreen, drinking alot of water/gatorade/accelerade/hydromax and eating energy bars and gel packs, wearing a hat, but I still have had trouble playing in this so much that Im literally suffering out there often which makes it extremely difficult to play my best and win against very good players. Im not able to move as fast and intensely like I would if I was feeling better. Ive lost a number of important matches that at least some would have been victories due to getting what Id call heat sick/fatigued. If I could figure out what the exact problem is and how to combat it, Id be able to get so much further. I dont know if I simply need to do better and more of what Im already doing, or if I need to do more stamina and endurance training, or if im not getting enough sleep or taking enough days off, or if I have some sort of physical disability I dont know about, or if there is one specific thing I am missing or dont know about that I could eat, drink, take or do or whatever to fix it? Help is greatly appreciated and Id be forever in debt to the answers.