Sometimes when I m trying to sleep my heart starts beating really fast and it only happens once in a while but it s been going on for like about a year and then last night my heart started beating pretty hard/fast in like less than 2 seconds but I felt really uncomfortable afterwards. There was a situation around September ish of 2014 where I was at school and throughout the day my heart would randomly start beating fast/hard. And each time this happened, I had to breathe in really hard for my heart beat to slow down. I don t know if I should go to the doctor.. Maybe it s anxiety or the junk food I eat(I m a teenager, 17) but I highly doubt it since I only weigh around 135 lbs.