Do you know what the dew point was when you were riding?
I try to avoid any serious exertion if the dewpoint is in the upper 60s to 70s. That is just too humid. You can be dripping sweat, but if the dewpoint is in the 70s, your skin can't cool below the dew point temperature so if you are trying any high wattage exertion you might have trouble shedding the heat you produce. In such conditions, you need to keep your wattage levels reasonable.
More on dew point here:
https://www.weather.gov/arx/why_dewpoint_vs_humidity
I did a bike tour in Everglades and Florida Keys in Feb 2017, dewpoint was usually around 70 degrees (F). Thus oppressive all the time. We did ok even though we live in Wisconsin, thus had zero time to acclimate our bodies to hot humid weather, we went from dead of snowy winter straight to hot humidity. We kept our energy expenditure at reasonable levels and tried to avoid over-exerting ourselves and that worked for us. And, on the days with the most oppressive heat forecasts, we tried to start riding as soon after sunup as possible so we could quit before it got really hot.
If your weather forecast sources do not tell you predicted dew points, find other forecast sources.
Photo on the morning we rode out of Everglades, soon after we started riding in the fog with sunrise in front of us, outline of my touring partner riding in front of me. I had both my taillights on in flash mode for obvious reasons.
