@VaccineAnxiety I don’t know if this will help, but I had an episode of sudden breathing problems after my first vaccination - but not caused by the vaccine. I’d actually been having these episodes since before having the vaccine and already had a referral to a specialist - so these problems were NOT caused by the vaccine. Just wanted to be really clear about that! 
I called 111 about the breathing problems and they asked me to immediately go to hospital in case it was a clot caused by the vaccine (I knew it wouldn’t be, as the symptoms had started a month before I had the vaccine, and I don’t think it’s mastered time travel yet!) but went along anyway. Hospital looked after me brilliantly, I had a d-dimer (blood clot) test which came back clear, blood tests for other things, and a chest x Ray, and was home again in about 10 hours.
Now in my case I knew it wasn’t related to the vaccine, but they treated it as if it were. They knew exactly what tests to do, did them quickly and were ready to do a CT scan if the d-dimer had been borderline/positive.
So, worst case scenario is, if you notice any symptoms, and end up going to hospital they know exactly what to look for, and if they found any issues would be able to treat you on the spot.
Sorry for the long winded post, I hope it helps though. And good luck! 