I had asthma when I was younger and frequently used an inhaler. Half way through high school, I played sports and grew out of it. I didn't need an inhaler again until 10 years later (now). I was never a smoker, never did drugs, nothing. 
I've been experiencing with edibles for my joint pain and recently got into smoking. I started smoking joints (paper) and my asthma came back. I was smoking for about 3 weeks. I quit. I switched to edibles/tinctures again and I felt like it didn't help my pain as much, just put me in a body high. I than switched to vaping, the first few days were fine. I started noticing I was very congested in my nose, my acid reflux was acting up, chest congestion,etc. so I quit 2 days ago. Well around the same day I quit I started having really bad heart palpitations and chest pressure, I was at a 95 heart rate sitting down. 
Went to the ER twice, they did an EKG and said everything was fine. Did an ultrasound, didn't see any fluid or inflammation. I'm out of shape, 5ft 135 pounds. But I'm at the point where now when I talk I feel out of breath , walking up the stairs my heart races. Sitting down feels worse than standing up. 
What could this be if my EKG came back fine???