Judgment is the first thing to go in both heat illnesses and hypothermia. You need to watch out for your companions and make sure they are educated on the dangers and watching out for you. Going solo is taking a risk, even on a day hike.

And people under-estimate the risk. One can suffer heat exhaustion doing winter activities....

It wasn't that long ago that an SAS candidate got lost and died of hypothermia in a cross-country training exercise.