On holiday in Jersey I ended up being whisked to A & E with a supraventricular tachycardia. To try and get the heart rate down from a pretty constant 230 bpm (it had been much higher initially) I was asked to lean forwards, hold my breath and push down as if trying to go to the loo. It was hoped that this would get the heart rate back to normal but wasn't successful and ended up with a couple of injections of a drug to reset the heart. Overnight in intensive coronary care and a couple more days in hospital for observation, not a great holiday! Anyway, to get to the point, sounds rather like the Valsalva maneuver.