I had exactly the same thing. I smoked a blunt with some friends in the woods. I took a lot in that day which was not a good idea. I had to leave them and get home while I was still high. After 15 minutes of walking home I started getting these unpleasant sensations followed by racing heart and palpitations. I also started getting these hot flashes and hills and it wasn't even cold outside. I had honestly had no clue what was going on with me. I too thought I was having a heart attack. My chest was really in pain. Finally my legs started to shake and I thought I was going insane. I didn't know what to think, because it was my first time having one. My body was definitely not used to these feelings. My panic attacks would go on and off. At first I felt like c**p, then I started to calm down again. However, they kept coming back, but less and less strong each time. This whole cycle/process lasted about 1 hour for me. After it was finally gone, I felt fine for about 3 weeks. Then all of a sudden, as I was laying on my bed watching TV i had another one. That time I knew what was going on and it only lasted for 20 minutes. They were the same feelings I had the first time, but a little weaker and less agonizing. After it was gone though, it left these symptoms of chest discomfort/abdominal discomfort and it kept me constantly restless. Of course these symptoms died down. However these symptoms keep coming back to this day making my life hell. I have not had a major panic attack since that second time, and I hope I never will again. But I keep a constant fear that they will come back, which usually puts me in distress and gives me those symptoms chest and abdominal discomfort and occasional heart racing.
As someone who has had a lot of panic attacks, I can tell you that they're nothing to fear. Oh sure, they feel terrifying, but there's nothing going wrong with you while you have one. It just FEELS that way. Have you talked to someone about this? A therapist can actually help you a lot. Have you considered it?