Heart palpitations and physical anxiety.

I was prescribed Methylphenidate extended release last month for ADHD. After my 9th dose, I started feeling extremely anxious PHYSICALLY. I haven't taken my medication in almost 3 weeks and I still get panic attacks nearly every night and during the day, I have very uncomfortable heart palpitations and vibrations all over my body. It feels like I'm sitting in a still car with the engine on. I'm doing yoga and I'm taking magnesium supplements but nothing works. (Note: My physical anxiety symptoms trigger my mental anxiety and not vice versa). I don't think about anything that would make me anxious but my body still feels so uncomfortable. Is there a solution to this impending doom or will I have to live this way for the rest of my life?? Please help! I don't know how much more of this I can take