Thats super interesting I've never heard of this before. It seems that toxin gives a persistent increase in the activity of the sodium channel(s) that make cold painful. I imagine similar to how cold water on frozen fingers feels burning hot.

Several years ago I went to a talk about a receptor (TRPM8) that is activated by cold and also minty flavors(!). Would be curious to know if your friends experience(d) mint as burning/uncomfortable. If not, it would suggest the pathology is linked to separate cold-sensing physiology/pathways/neurons than the common "cool" feeling most are familiar with.