I had open heart surgery when I was 4 years old. Nothing serious (well, it could have been worse) to repair a hole in my heart.
I started developing palpitations and began getting light-headed after I graduated high school. I had checkup after checkup after checkup after EKG after procedure, etc. All saying my heart was perfect and I should experience no heart problems ever for the rest of my life...my heart is healed.
It wasn't until I spoke to my family doctor when he said that it was anxiety. Some days I will have palpitations a few times, and sometimes I will go weeks without having one.
Imagine how messed up this made me before finding out. The combination of open heart surgery with anxiety can be a horrible combination.
I still go to the hospital sometimes when I am having really bad anxiety and they just lay me down in a hospital bed, I fall asleep exhausted, and wake up fine.
Long story short, your mind is capable of very powerful things. I am a musician so I now pick up my guitar or play a game to avoid this happening all of the time.
I wish you the best, and just reassure yourself that everything will be okay