Does a defendant have to testify during the trial of a convicted murderer who was prescribed an anti-anxiety medication while still under the effects of his medication?

Defendant contends the trial court violated his right to due process by insisting he begin testifying when he was still under the effects of his medication. (See Riggins v. Nevada (1992) 504 U.S. 127, 112 S.Ct. 1810, 118 L.Ed.2d 479.) He claims that the side effects of his medication caused him to appear emotionless, remorseless, and uncaring during his testimony, which led the prosecutor at the guilt phase and penalty phase closing arguments to describe him as "cold as ice" while testifying, and the "ice man" who "doesn't give a damn about the victims" and "shows no emotion."