Big hug to you. That's no fun at all. I totally get the vulnerability you feel about the shoulder - that second break was just so fluke-y!

I had a similar throat closing up experience - right after I started riding again last year after being off the bike for 6 months from the pulmonary emboli I had. I did a ride with DH and friends, who were all stronger than I was/am. We got on a rolly road into a headwind, and I just fell off the back and watched them get farther and farther away. I could feel my throat starting to close up as if I were going to start crying, and I just had to back off the speed, not look at them, and do deep slow breathing to keep myself from starting to hyperventilate. Like my thing, yours "may" be in your head. But a rescue inhaler couldn't hurt.

The story about the horse mutual escalating panic attacks gave me a good chuckle. Been there! (In my case, augmented by the Arabian factor. )