So I have been very, **very inactive for like 2 years** now, because of my health anxiety, GAD, and panic disorder. Recently I out of nowhere started to go on daily walks for like 1-2 hours straight, which i felt helped and calmed me alot but, i started to feel this tightness/heaviness/pressured feeling in my chest and upper abdomen slightly getting worse and worse. Today I really feel like having an undiagnosed heart or lung problem. This constant feeling of heaviness and shortness of breath is not letting go. And for me having health anxiety for so long, this feels kinda different, but more because i dont get the regular breaks where I feel 'OK'. I took 2 ECGs in june/july for similar problems/sensations, and they turned out completely fine. After this my doctor has also listened to my heart and lungs which also turned out fine. Bloodpressure was 120/69 the last time i checked. I have a very low pulse, even when i have a panic attack i can have like 55 pulse because at the very start of my anxiety problems i tried to always breathe slow, so I rarely hyperventilate. I also excperience pain in my ribs, back, neck etc. Sorry for the long health journal of problems i just cant really get my head around this. I want to believe its just a combination of long lasting anxiety and muscle tension, but i always think it is something way worse since it never stops. I also called the ER, not visited, and they told me it was just anxiety and started talking about relaxing methodes and mindfullness, i just find it hard to believe people when im like this. I dont know what i should do with this.. :/  
Btw im a 21yr old male, and this is my first ever reddit post.