I Am Experiencing Rapid Heartbeat Even When I Relaxed

I am 19 years old, 5' 8 120 pounds. sometimes my heart rate is very rapid even when im completely relaxed. today for the first time ever I experienced what i believe to be a palpitation. heres how I described it to my mother. it felt like i was double breathing. like i would take a breath and the double would feel like a bubble expanding in my chest and i would have to take a deep breath to make it go away, then i took my pulse and after the double beat it would be rapid then it would slow back to normal. this continued for about 3-4 hours. i wondering if what i felt really was a palpitation?