If you’re having heart palpitations, you can usually get them to go away by exhaling heavily through your nose and then holding your breath. You’ll feel your heart beat like normal and won’t have any more palpitations after.

I think it has something to do with carbon dioxide levels in your blood, but holding your breath can cause your heart to start beating normally again when it gets palpitations and feels like it’s going to explode. Just breathe in and out normally after, and remember to take your time and get a nice big deep breath.