First, as general information, I am a 17 year old male and I have never had any major health problems before (nor have I ever done things like take drugs, have sex, etc.)
The other day in school while I was sitting in my class, I passed out. As described by my friends later, fell over from my desk (my head did not hit the floor), my legs shook for a second, and I was back up within 5 seconds. I did not expect it at all, and my only complaint would be the second before I had a slight pain in my chest. Nevertheless, it was suggested that I go to the ER to be checked to see if anything was wrong. At the hospital, I had an EKG performed and a chest X-Ray and I was told that all was well, and I had probably fainted because of stress (for the record, I am in 3 AP classes, I am self studying another 3 AP tests, I had SATs the next day, which I ended up taking, and my father had died four months ago on that day). Nothing more was really made of the situation.
This happened on a Friday, and I was fine until Monday. At that point, it seemed as if thoughts of this or something more serious dominated my mind. Then, I started feeling slight pains throughout my body, which I tried to think nothing of, but my fear after fainting made me amplify my thoughts, but I generally still felt that nothing was wrong. Today, Thursday, I am starting to feel more worried. Since last night, I have had a strange feeling of "gas" coming out of my heart area (left chest area). It is by no means painful; it just feels like a "burp", with my left chest being the source of the gas instead of my stomach. Today, I had to do a somewhat stressful lab in Chemistry that required me to walk from the front to the back of the room several times. At the end of the lab, I was all but winded and I feet extremely tired and worn out and I could not catch my breath. Likewise, I felt this gas coming from my chest area, as described above. In addition, I had an extreme urge to pee, but I could not get up at the time. After another period, I felt fine, as I do now. I am just getting really worried that this is something more. It has come to completely dominate my thoughts, which also makes me think I could be amplifying this situation since it is the only thing I can possibly think about. Is this something I should be worried about, or is it really nothing? Any help would be greatly appreciated; thank you in advance!
EDIT: I also should note that I have a family history for heart disease, from both sides of my family.