I also suffer from this problem. I doesn't happen every day. Probably more like a few times every month. My pulse goes up from 55-60 to 120-130. My Apple Watch recorded a pulse of 125 from 5 am to 11 am. At 4 am when I also was asleep my heart rate was 57. I also suffer from a blocked nose. It is not always blocked when I try to sleep. It can be every night for 2-3 weeks. Then it is clear for a month. I've tried different anti-allergic sprays and tablets. Not sure if my high pulse is due to the fact that I can't breathe with my nose? My GP says that if the body was in desperate need of air it would breathe with the mouth automatically. I've woken up a few times feeling that in desperate need of oxygen. But when I had a pulse for 125 for 5 hours straight I didn't wake up. I felt like s*** when I woke up, and I felt that my sleep was very bad. I felt that I could remember some of it. I had a slight sleep apnea a few years ago. Removed my tonsillitis. I think it helped. But that was 5 years ago. Haven't done a new sleep test after that. Have you guys tried an oximeter?