When I was a junior in college i went through a similar situation myself. The first time this occurred seemingly out of the middle of nowhere in the evening I thought i was having a heart attack. I calmed myself down and tried to assure myself that I was wrong, that I was too young and healthy for that.
Over the next few days and weeks as symptoms reoccurred, I felt like my life was falling apart. I was convinced something was physically wrong with me but couldn’t seem to figure out what it was (which was by far the most disconcerting part). I went to multiple doctors appointments and once to emergicare, started recording everything i ate thinking that perhaps i had developed some serious new food allergy, and in general just felt like I had lost all reliable function of my body’s emergency systems. Basically I felt like I was completely drowning for a good 2 or 3 weeks and ended up losing something like 15 pounds in that time. I remember being so depressed and anxious and trapped inside of myself, constantly hyper-vigilant for any odd feeling that might occur in me.
I guess eventually I got “over it” (kinda) by just facing it head on. I remember thinking id rather die of a heart attack or whatever around people than sleepless and terrified in my bed so I just gave up all caution (had previously been afraid to even walk much and risk setting something off) and started running on the track at my school until i was exhausted. Which gave me some confidence that if I didn’t die from that, I was unlikely to die from sedentary activity. Finally I just got used to my body feeling out of whack occasionally. I stopped monitoring myself for symptoms so much.
I had a hard time accepting that my symptoms were largely psychosomatic though it seems you don’t have this difficulty. That’s one thing in you have going for you at least. My advice to you would be: just to do what you have to to get back in a healthy state, be serious about it. oh and exercise too.