Teenager scared of having a heart attack(HELP!!!)?

Wednesday morning I was feeling nauseated and dizzy. I had lost my appetite even though I eat breakfast promptly every morning. I told my mom that I thought I may be anemic and I told her to make me a doc apt. Note that I am very athletic and workout 4-5 times a week an hour-hr/half each time I go to the gym(ranging from cardio to weight lifting). The lady at the hospital asked my mom how my weight and height (110 pounds, 5'8) and the lady said that I should come in ASAP because she said it sounded as if I was anorexic. I laughed hysterically at this because I eat very healthy. Fruits & veggies with every meal, ect. Just basically I know I am healthy and know I AM NOT ANOREXIC, no need for details. Anyhow I end up being sent to the hospital because my doc had ran an EKG on me and my heart rate was 44 just lying there. So she told me I needed to be admitted to the hospital ASAP. I ended up being in the hospital for 3 freakin' days on anorexia protocol with a sitter with me 24/7. Anyhow, my heart rate kept going down really low while I was sleeping(lowest was 36) and I had to stay there and drink these shakes 4 times a day so my heart rate would stay over 45. I just got out today and am having serious anxiety. I feel like I came really close to death...and still am. I'm scared to go to sleep because I fear that I will not wake up or possibly have a heart attack even though I'm only a 15 year old female. I'm experiencing shortness of breath, and feel like something isn't right with me. I feel different. I really have no clue what to do. I am researching and ran across something on Myocardial infarction. Could the docs have not diagnosed me with this because they weren't sure what to look for?