Henry, I'm up in the wee hrs. to catch a plane to the Grand Canyon for a bucket list backpack, so all I can say is I'm glad we helped a little. I read some stuff on line- just research "night sweats" and "sweating in the groin" and a number of good explanations come up. I was surprised that cotton briefs are called for, rather than any type of boxers. I've got one more suggestion- keep your head warm with a hat so you don't need the warmth of the bag quite as much if you aren't doing that already. My best wishes for a solution!