I had a bad case of postural bradycardia for about 3 weeks 15 years ago. It came on after I rode home from a trip to California and fell asleep for a hour or more with my head tipped forward with my chin on my chest. I could barely stand up during the first week or two. My pulse was staying below 50. I just slept or dozed most of the time.

This was before I discovered that my upper neck was getting inflamed and interrupting my autonomic nervous system every time I had a head forward posture for an extended period (10 minutes or more).

My chiro and PT helped reduced the poor alignment but the most important part was being disciplined to no sleep or rest with bad posture.