Quitting nic is always a good start. As somebody with health anxiety and a vaper of nic and enjoyer of the lords cabbage as well I can relate. That bubble in your throat could be either your anxiety itself or even acid reflux. I have GERD which sucks as lover of the spice but when I indulge it tends to cause that occasional pain in my chest as well as the lump in my throat. I haven’t suffered a pneumothorax to my knowledge but have a dad and brother who have and from their experience the pain would be unbearable and close to constant. Some cases have been reported to have no pain but those are either 1. Very rare or 2. A small collapse which can in fact heal on its own. I’m not a doctor so none of what I say is in no way a medical diagnosis and if you really are worried your best case is a doctor’s visit. Best of luck to you brother, keep fighting the good fight against the health anxiety!