I mentioned before. One early sign is you stopped sweating. I suspect this is a point of critical dehydration. I experienced a few times. Being a heavy sweater, my palms will be wet with sweat. Then suddenly I realize they are dry. Immediately stopped and seek hydration.
For me is also it "suddenly" becomes too hot. Probably also somewhat related to the perspiration (less cooling).
I kena once before, not during exercise but kite flying at MB area, which is a fair bit warmer at the rooftop area. I was trying to retrieve my big kite also, so got physical exertion. After 30 mins of trying.....finished liao, but felt super duper warm. Heng finished, so could take a rest + pour water on myself to further cool.
Those times the RH% also not high coz 3-4pm, so can evaporate one.
Then during my first 10k fast + PB attempt, i also somewhat kena.....not as bad as the kite flying that time, but still i could feel that the heat was a bigger drag than my breathing/cardio effort, which of coz then signalled me to stop and pour water. After that no more of those evening runs during warm months....in fact even zone 2 longer runs i won't do one, just not comfy and not for me.
