No, this is the "you don't know anything about how Parkinson's medications work" bit.
Withdrawal from Parkinson's medications cause rigidity, not increased mobility. The medications are not precise in their effect, and can vary from day to day, since they are designed to regulate dopamine emmissions from dying nerve cells, which notoriously don't send two weeks' notice when they each quit.
As A.S. Yeti, Esq., pointed out, the medications have other side effects which one may want to avoid during a long period of testimony. That has nothing to do with shooting a commercial.
Limbaugh didn't bother to check his facts before shooting his mouth off, which is no surprise to me. What I find interesting is that you attempt to excuse Limbaugh's willful ignorance by blaming Fox for speaking up.