Hi ... yes, definitely many symptoms to a steroid injection (red flushing, heart rate goes up, nauseasness possibly) ... I, too, have impingement of the right shoulder along with many other problems and have had the steroid injection at least 5 times, possibly 6 times now and will have one more injection next week ... the drs. do not like giving out this many injections because it can start softening the rotator cuff and make matters even worse (most drs. will do 2-3 injections) ... so I'm scheduled for surgery in a few months. I've had this problem going on for a few years now, but the first year the dr. would put on an "iontophoresis patch" with each visit which would help just a little ... not sure if your dr. has tried that with you (it looks like a very large bandaid and on half the bandaid is water and the other half side the dr. puts some steroid on it, places it on your shoulder and then puts a charger on the outside of the bandaid to help in aiding the solutions into your shoulder).
As to your flare-up, I understand your pain as to my last injection done by a different dr. was unbearable ... he did the injection at a completely different site of the back of my armpit vs front shoulder and about 10 minutes after, my shoulder started getting worse and worse with pain ... anyway, they call it possibly an injection flareup or the needle could have actually hit one of the nerves in the shoulder.
I hope you're feeling better from your injection now :angel: