I have Raynaud's Syndrome. Occasionally, my fingers will lose all circulation.

I stick them under my husband’s arms and steal his warmth. Or if he is not available, I’ll use warm water or just my own body parts that are warm.

I actually have this too! For me, it usually happens when my extremities get too cold, and it can take me a bit to even notice it's happening. It usually happens predominantly in my big toes for some reason. For me it just feels like like it's gone completely numb, and I lose all feeling in the digit. I usually break out the heating pad and try to warm it back up until I can feel it again.