knees blew up like balloons, what can you do when the heat prevents one from knowing they have overstretched??

I just cannot figure how to protect my knees. Memorial day I could not hike w friends as my knees needed icing to get back to size. and just now the knees blew up again and almost could not do scuba.. you have to get up the ladder.. my knees never blew up like this before taking Bikram yoga.. how do you protect your knees please..
I have hiked and hiked before this yoga never had so much problem w my knees.
now half moon.. i do not lock the knees when bending over, now I contract my thighs and try as hard as i can to get my face down on my shins so no light can come thru as the instruction says. My knees blew up again. just before the scuba vacation. thank god we were driving to the Florida keys.. so I iced then for 3 days and was ok to dive.. just the knee swelling never happened before .. has to be the yoga..
also how do you stop overstretching ones arms.. since you do not feel the overstretch in the heat? is it ok to modify the poses as not to strain in any way.. or just find another practice to keep one limber and flexible..cause the heat prevents one from knowing they have gone to far.. i like the heat getting all the toxins out. Must I tell myself to just do posture don’t care about the pose