low resting heart rate

[Fondant]

I’m probably worrying over nothing but here goes……my normal resting heart rate is normally between 50-60 beats per minute, I currently have COVID it other than sniffles and a slight sore throat I feel fine. The worst was 2 days ago when I had a bad cold, headache and general flu like symptoms. Like I said I’m feeling fine now but still testing positive. But yesterday and today I’ve noticed my resting heart rate (mainly when sleeping) has been in the 40s. One of the readings overnight said it actually dropped to 40bpm. These are readings from my Apple Watch and it’s saying my average resting heart rate is 45. Should I be concerned or does anyone else have this?

can I also add for the past 2 weeks I have been on the KETO diet and already lost half a stone.