High and low spikes in my watch

I got the Nike Apple Watch for Christmas and all seemed good for the first week. Then I noticed whilst doing an excercise that I normally do , my heart rare had apparently hit 195 then dropped very low before getting back to my normal. Which I found strange as my heart certainly wasnt going that fast. Now since then I have seen peaks when my heart is apparently at 185/175 briefly then drops very low suddenly again. I was putting washing in the machine and cooking on another occasion and wonder if hand movements can affect the heart rate monitor. My heart certainly wasn’t going that fast. My resting heart rate is fine and when I run it is stable, but the peaks and drops are really bugging me as they seem to just crop up for no reason. I have had an ECG in the last 6 months and all was fine, but this is really putting me off of the watch.