our neurologist explained that tics feel like urges that they have to do, kinda like an itch. So your son's explaination of needing to pop the balloon makes sense.
Anxiety is a trigger for my son as well. While we were on vacation this past summer, we stayed on the top floor of a hotel. Every time we left the room he glanced through the railing down over the edge and would have a verbal tic that was a quick "er". It was one of his tics that has come and gone a few times now.
My son has bad allergies and asthma as well, grass being the worst. Allergy and decongestant medicines are triggers for him. Singulair and benadryl being the worst. He can take levocetirizine and nasal sprays for a short time without problems. He also gets allergy shots at the moment. He had very bad verbal and motor tics back in October and we think it was triggered by an increase in the concentration of the dose as well as the frequency. We just started getting the shots again but giving more time between shots. We are nervous about starting them back up but they have really helped his allergies and asthma.
I'll include your son in my prayers!