This might be a bit weird, but I just wanted to share it somewhere and thought 'casual' might be a good place.
I will sometimes have a few hours or even a day through which I can feel my heart palpitate every few minutes at random. This has always worried me because my heart is... well... rather important to me. I once spoke to a doctor about this, but there was nothing to measure because I can't trigger these events on command. The doctor did say that palpitations are common and usually benign.
Still, it bothered me to not know specifically what is happening with my heart when I feel a palpitation. So, about two years ago I bought a small personal electrocardiogram monitor. This morning, finally, I woke up with palpitations. I stuck the leads of the ECG, monitored for a few minutes, and was able to measure my heart as it palpitates!
In the image that I have attached, you can see that in between the regular beats there are a few irregular beats that are closer than usual to the preceding beat and have an extra deep depression and a broad and tall peak. With this image I was able to do some online research and figure out what I am observing: a 'premature ventricular contraction', or 'PVC'. Basically, shortly after a hearbeat a second heartbeat is triggered from the other side of the heart. This delays the following heartbeat, causing the next heartbeat to deliver an even stronger beat. The delay of the beat makes it feel like a 'skipped' heartbeat, and the following heartbeat is stronger because there was more time for the heart to recover - this is felt as a palpitation.
I found [this](https://www.youtube.com/watch?v=1LKg7d2gd-Q) video on the topic to be very instructive. It turns out that these 'PVC's are quite commonly present in healthy individuals and they are general demand. They may sometimes have an underlying cause such as an electrolyte imbalance, but stress, lack of sleep, and coffee can cause them too. Unless they occur continuously over a very long period of time, they are generally not a problem.