My wakeup HR is dropping as fast as it went up last week! It was 51 this morning. I think I've figured out why it went so high, and the cause is related to lack of sleep. A couple of weeks ago I didn't get enough sleep for a night or two, and I picked up a slight cold. My nose dripped a bit and I had an occasional cough that brought up thick, green stuff. My nose was dripping thin mucus. As far as colds go, it was a slight cold, but my HR went up. My cold is pretty much gone and my HR is coming down.
I don't get colds very often. Before I started running, I got several bad colds per year. Then one day I realized I wasn't getting colds anymore. That was about 25 years ago. Even though I'm at an advanced age (69) I don't get flu shots since I have a strong immune system. The only time I get a cold is if I get insufficient sleep or overtrain, both causing my immune system to weaken.