For me personally, I have similar issues being dehydrated quickly in open sun. My mother pointed out to me that she had "hyperhidrosis", or excessive sweating and that opened my eyes in a lot of ways. For the two of us, it shows up as cold and clammy hands and feet to show poor circulation and my sweating is mostly hands, feet, and armpits with limited sweating in other areas. When I'm out in the open sun for too long with no cloud cover, my body sweats out as much water as it can, leaving me excessively dehydrated.
For a remedy, I always search for "herbal legacy" and Dr. Christopher and here is the article for circulation issues below. Cayenne pepper is supposed to be one of the keys for a long life and great for circulation. Malfunction of the sweat glands (if that's what you might have) is also related somehow to nervous system issues I believe and there is a set of herbs related to helping with the nervous system as well.
https://www.herballegacy.com/Blood_Circulation.html
https://www.herballegacy.com/Nerves.html
Hopefully this helps someone who may not have heard about hyperhidrosis - I still have the poor circulation, but do make a lot of compromises in what I eat for balancing the crazy busy work weeks, cost of foods, etc. so there are still toxins from the food system that accumulate and a good detox program could also help clear out toxins affecting the nerves. I am a fan of the green smoothie diet by JJ Smith, I noticed general improvements with my whole body after following that plan several years ago and just made a note to go back and do another round in the next week or two once we gather all the ingredients again.