RAPID HEARTBEAT. Anxiety?

First of all, God bless y'all for taking the time to read this. I'm a 27 y.o male. I have been very active all my life and I'm very fit. About 3 years ago I began using marijuana for recreational purposes. I loved it. It was my last two years of college and it helped me focus, helped me be more creative and it helped me with depression after a horrible break up. One night after smoking I had the worse experience of my life. My heart began beating uncontrollably. I freaked out and panicked. I tried to calm down but I found it to be impossible. I then became disoriented, got a weird feeling in my left arm and behind my left ear. I thought I was having a heart attack so I was rushed to the ER. I was in a constant state of "deja-Vu" this whole time. I was told at the hospital that my potassium level was extremely low. They ran a bunch of tests and measured my heart rate twice with an EKG machine. I ran for them for like 15 minutes and they said I was ready for a marathon. I was given a beta blocker which I stopped taking about 2 weeks after the incident. About a month later I tried marijuana again and got a similar attack, very short this time. I panicked once again but I calmed down. Felt like c**p for about an hour and a half. After researching online I found out a lot of people had the same problem and they were told they were having anxiety and panick attacks. Ever since I stopped smoking marijuana. It's been quite a while now since I haven't smoked. Okay now to the part that intrigues me ... This morning I was sleeping. And in the dream itself I was feeling tired. Like I was tired of being asleep and felt like fainting. This woke me up. Later that night/morning I felt the same way and woke up nervous. My heart was raising fast. I lost hearing for about 2 seconds and became disoriented again. This attack felt very similar to the one I had the first time, just very short. Lasted for about 5 seconds. After this incident, I began yawning a lot. I began shaking as if I was freezing and had a weird sensation in my chest. I tried to go back to sleep but all i could feel and focus on was my heart. I had a bit of trouble keeping the rhythm of my breath. This worried me because I haven't smoked and usually it was the marijuana that triggered these type of attacks. Yesterday I had a sharp pain in my chest but only when breathing in. Also I've been having a lot of heartburn the past couple of days, but then again I've been eating horribly lol. I'm not sure what could be causing these attacks. I don't want to have another event where I wake up with this nervous feeling and right after my heart begins raising like crazy. I thought I was gonna die and all I could do was ask God to please don't take me away just yet. Any ideas what could be causing these attacks? I originally thought it was the marijuana so I stopped. But now I'm thinking it might be something else since this is the first time it happens without using it.