I skipped my bisoprolol med yesterday.

I skipped my bisoprolol medication yesterday and today. My cardiologist prescribed it to me because i kept having really high heart rate in public. And the medication actually helped alot. I forgot to take it yesterday and today too. I went outside in the sun at 2pm walked for atleast 10 mins with a really accurate heart rate monitor. At 5 mins my heart rate was at 145 and by 10 mins it was at 190bpm. The machine said my heart averaged 145bpm during this and peak was 189bpm. I felt like my heart will explode while standing still in the building elevator. Came back immediately layed down on my bed the heart rate slowly came back to 120bpm and 92bpm a minute after. I also have the machine on whenever i go outside this rarely happens. Usually goes as high as 150bpm while walking up a slope or stairs.Am i really sensitive now or is this an underlying issue?