Propranolol works really well for some people. It sort of mops up all the chemicals that are involved in the viscous circle of anxiety reactions.
I think the problem you may encounter, is the fact that you are taking it on "as required" (PRN) basis, which could cause some uncertainty for your AME.
It may be a good idea to revisit your prescriber, and inform him of the implications of your prescription.
As Radgirl states, there maybe a better solution :-)