High resting heart rate - any ideas?

Hello everyone,

3 years ago I was in amazing shape and my resting heart rate was around 50-60.

It’s not exactly clear if that was the case due to uncertainty on the bloodwork, but I tested positive for EBV reactivation and physically I was exhausted. Certainly felt like mono. Quit running completely and no exercise for 6 months.

Training’s been inconsistent ever since as I seem to frequently get some setback now and then, but I should be overall healthy with weights 3-4 times per week and brisk walks on off days. Had 3 consistent months start of this year before I got ill again.

Just like 3 years ago I’ve had an elevated resting heart rate this year, too. It can go as high as 100-110.

Typically around 80-85. Upon awakening it can be as low as low 60s.

Any ideas? I’ve thought it could be some viral infection which is slow to let go. Maybe undiagnosed allergies as I seem to be ill with colds frequently.