Vívosport heart rate drops

Hello. I have vívosport (v. 3.90). I guess it's not a big deal but it's been happening more and more lately and I was wondering if someone else has been having the same or a similar issue. My heart is sometimes shown to have dropped down to 40s 50s (from 60-80) and after a few minutes it goes back up (I don't recall feeling dizzy or anything else like that). At the same time the stressmeter shows very low value (0-5) regardless of the previous stress value (even if it was 40-50 for some time) and also goes up after a couple minutes. It usually happens while being excited or stressed out especiallly when playing video games. It almost never happens while being active. Thanks for your input.