Correction: When I wake up in the morning I have zero back pain.
When I was a younger man I was diagnosed with AS. It took awhile to get the diagnosis correct but the genetic test confirmed that AS was the cause of my extreme joint discomfort. It's a very stressful disease as you know. I did have rapid night heart beat, much higher than yours and night sweats, but it was then diagnosed as stress, I worried greatly what would happen with my work, the kids, family, etc with me incapacitated. I was told that heart symptoms with AS would be an end-stage problem. Gradually as I aged my AS symptoms disappeared, and now when I wake up in the morning I have zero heart pain. AS problems tend to disappear the older one gets.
That being said, I now have loads of heart problems, so I don't really know the role AS played. However, I tend to think that the fact that I smoked cigarettes, ate lots of patty melts, etc, had a whole lot more to do with my late-life heart problems than AS.
AS progressed from my spine to my neck and I don't have much motion there (but no pain) and evenutally froze up my sternum. I get sternum pain when I exercise too hard, and it masked my first heart attack. It's important for anyone to remember, if you can press hard where chest pain occurs and it hurts worse, it's not the heart.
I'd get my heart checked out with additional tests, but I'm betting it's stress. Hang in there, keep us informed.