Singapore GP said it was the likely cause given the symptoms and timing. I also have video showing my my government-provided heart/oxygen monitor skipping beats (and multiple readouts over weeks indicating irregular beats)... see below. That only started a couple of days after the booster. Up to July 31, 2021, there were 9,400 post-vaccine adverse events in Singapore... and these are only reported cases. People receive from S$2,000 to S$250,000 compensation from the government for confirmed adverse events. They've stopped reporting the number of adverse events in the media this year. BTW, I did not apply for compensation.