Propranolol Side Effects? please advise

I've been on 40mg of propranolol for social phobia for about 3 years now, and have been taking them as and when needed. My routine is currently 1 a day for 4 days and then none for 3 days because the first 4 days are my days at university.

On Thursday on the bus home I was feeling completely fine & relaxed and then all of a sudden I felt like I was going to die. I had a tightness/stiffness in the throat and a sensation that seemed to spread throughout my head. Like my brain was gradually shutting down. It lasted for a couple of minutes but was really scary stuff. I was so close to asking the man next to me to help me. When I got home eventually I cried and cried with the shock.

I was then completely fine over the weekend. Today, I was back at uni so I had another propranolol before I left. I had the same thing on the bus there and felt really weird throughout my lecture, and then I was completely fine again until 5 minutes ago when, sitting on the sofa, I had it again. The wave of cloudiness spreading throughout my head.

Im really worried because I have never had any trouble with side-effects from propranolol before, but it only seems to happen in the last few daus when I've just taken one or am coming off one.

Im also really upset if it is the propranolol because obviously I'll have to stop taking them and I'll have to go back to not being physically able to speak to anyone at all at uni.