See if he is inhaling while he draws. If he is that could be causing it. Tell him to draw the vapor slowly holding it in his mouth when he gets a mouthful then inhale. You know how you drink from a straw and as your pulling the lets say soda you cut off your throat with your tongue until your ready to swallow, same principal. Draw your vapor in your mouth and hold until your ready and then inhale. Hope this helps would love to see another person say good bye to analogs.
I'm inclined to agree that this might have something to do with his issue, quite possibly combined with the anxiety factor. OR he might be doing what I did...at first, I was having some issues with dizziness and blamed it (very wrongly) on the PG/VG or nic in my cartridges. It took my son to solve the mystery.....I was holding my breath completely while drawing in the vapor, then did long exhales of it (if that makes any sense). It wasn't anything to do with formulas or anything else...it was me depriving myself of oxygen
I didn't even realize I was doing it and once I switched things around a little and got used to how to vape properly, dizziness went bye-bye....and so did the cigs.
I really hope that he manages to find out what's going on and can make the switch or at least use his PV to cut down on how many cigs he smokes a day. Best wishes on it, darlin' and kudos to you both for working on this together!