What Causes Shaky Feeling After Undergoing By-pass Surgery?

I had a double bypass in 2001. For the last few days I have had a very uneasy shaky feeling inside, sort of like when your sugar level drops low, but I can tell that it isnt my sugar. I have also felt very tired, almost to the point that it is an effort to walk very far. I have several other heath issues (psoriatic arthritis, severe psoriasis, thyroid tumor and the list goes on) and have not maintained a healthy lifestyle. Although I do take my medications regularly and watch what I eat, I do not exercise and I started back smoking. I recently started on Pravastatin and I was already on Lisinopril. I also take Enbrel injections. Could any of these medications be causing me to feel this way? Or could it be that the bypass has blockages and needs to be done again?