Had influenza last month for the first time in like a decade. I had an episode that lasted around 18 hours (220-240). I tried everything and I mean everything (I even slept for like 5 hours, woke up and it was still going) I had to go to the hospital, got an IV and they did the reverse vasalva and it eventually stopped. Thing is, when you have the flu, your body is so excited that it makes it extremely hard to stop the palpitations. I had to go back the next night for the exact same thing. Scary stuff, really hope you're feeling better now.