Another problem

Hi guys so Ive been on sertraline about two months maybe more, 50mg for about 5 weeks and 100mg for the Rest, about a week and a bit ago I was also put on 1.25mg of Bisoprolol. And I've not long been awake and I just took my pulse because I'm overly anxious of my heart and its counted to 54 bpm, now I'm worried because I've read that it shouldn't go below 50. I'm terrified because when Im not moving it's between 60-80 but as soon as I do any kind of movement like just standing up it's in the 100s, I've had ecgs and blood tests and had the enzymes in my heart checked and its all come back fine, am I okay? Should I worry bout my heart rate being at 54 right now

Anyone?

P