What is St. Elmo's Fire? I can only find a weather phenomenon.

I have a tactile perception of glowing all over my body. It's really creepy.

Could it be https://en.wikipedia.org/wiki/Photosensitivity#Skin_reaction... ?

This happens to some people with Benadryl as well (though doubt its related, just anecdotal). Curious - have you tried multiple (reduced) doses?

Benadryl is a first generation antihistamine which crosses Blood-brain barrier and makes you sleepy. Its mechanism of action is very different from melatonin and it has much more severe side effects (bad feeling after wake up) than melatonin.