Why should suicide be most painful?

Let's assume that Terri really would have wanted to die rather than live as she does. Let's assume that she wants her life to end. Would she have chosen this incredibly painful agonizing way to go?

We have testimony from a woman who was diagnosed in a vegetative state and starved (just like Terri). She says that it was agony.

So even if we assume she wants to die, why does it have to be this way?