I agree with @doorman about getting a short-term prescription of Valium, or Xanax to get past this temporary, but frightening episode. Both drugs work fairly quickly although Valium is slightly faster and stays in the body longer.

When I was regularly taking Effexor, if I missed a dose (I was on 25mg, regular-release, once a day), I would get a tremendous headache—a headache that was quite distinct from any others. Aspirin was my choice to deal with it, but your son can use whatever headache remedy he finds effective.

GABA supplements can improve sleep, ease anxiety, decrease muscle tension and boost mood. It is the brain’s main inhibitory neurotransmitter—it calms neurons (brain cells) and keeps the brain from getting overexcited.

Ben*dryl is an OTC antihistamine, but can be used as a sleep aid. I don't know if this is one of the OTC sleep aids your son found anxiety-inducing, but I took a 25mg Ben*dryl to ease the definite, shaky/"squiggly" feeling in my chest that I think was an adrenaline rush—that fight/flight reaction is quite bothersome and inexplicable when you know you're not in any danger.