Tapentadol
"I started taking Nucynta about 4 days ago. I took 1 x 50mg tablet that morning and I felt okay. I took another one that night and I had a terrible reaction, my face got hot and my heart started beating like crazy and the beats were very irregular. I thought I was having a heart attack. Luckily I am prescribed Klonopin, I had to take 2 of them and it took about a half an hour to stop. I almost called an ambulance."