I can't tell if it's anxiety or heart disease or digestion issues or even cancer.

This is quite long I am sorry but I just am so stressed about my symptoms.

One day I suddenly felt heart discomfort like there is pressure or tightness, not necessarily pain. I can really feel my heart pounding which forced me to take deep breaths in and out. I started freaking out and did not know what to do. Staying still made it worse and I started pacing. I started to feel scared and nauseous so I threw up and that me feel a bit better but I still had that heart discomfort. This lasted for hours and I did not get good sleep. I woke up the next day still slightly feeling chest discomfort and that feeling of anxiousness. Then it went away for a couple days and it came back. I had another attack and now I constantly feel chest discomfort as if I'm going to have a heart attack which I am constantly worried about getting or cardiac arrest. I went to the doctors to get an ECG and it came out fine, but I heard those can't guarantee that your heart is okay. Something I noticed was that i got these attack and chest discomforts whenever I ate. Now I don't have an appetite and can't eat in fear that something is going to happen to my heart, but I am hungry and wish that I can have a decent meal. So, I'm pretty drained most of the times and sometimes I get a wave of sudden fatigue out of nowhere for about an hour and then it goes away and I have energy again. Oh and it's always worse at night. I get anxious and chest discomfort in the middle of the night and can't sleep well. right now i started getting slight chest pain.

Please help. I don't know what to do. The other day I suddenly started crying and feeling depressed and lost because of this.  

Thank you for any responses.