Coffee is something that I am pretty much addicted to (probably drink a bit too much in fact) but it has given me scary physical effects before. When I was 19 I had developed agoraphobia and really bad panic attacks. During that time, drinking coffee could bring on a full-blown panic attack... which really sucked. I had to stop drinking it completely (didn't for an entire year).
Then one night last year, after drinking coffee (and just sitting on the couch) my heart rate skyrocketed super high and I felt sick. (I'm not sure why this happened - maybe because I hadn't drank any coffee in several days due to severe insomnia. I basically couldn't sleep at all and didn't want to make it worse with caffeine). Then once I drank some.... BOOM. Heart rate went crazy. It freaked me the hell out, and I ended up going to the ER cause my heart was going so fast I felt like I was about to have a fatal arrhythmia. After they ran tests, it turned out to just be benign tachycardia... so that was pretty embarrassing going to the ER over nothing (plus the EMTs that took me there assumed that I took drugs, which was kind of insulting).
Better to be safe than sorry though. Thankfully you didn't have permanent damage. I got in the habit of overdosing on coffee to the point where I felt like a heart attack was coming a couple times. Had uncontrollable shaking and felt terrible. I tried exercising it off and drinking a lot of water which probably wasn't the best treatment. One way they treat elevated heart rate in the ER is to push drugs quickly in your system which stops the heart for a few seconds to reset the rhythm. Sounds like a nightmare to experience.
Don't let people treat you like dirt.