It’s not that Will is weak; he is vulnerable. There is a difference. In the first episode, when Beverly interrupts him, he is in the middle of putting himself in Hobbs’ headspace. Because he has a vivid imagination, it’s easy to lose himself to fantasies. And as Hannibal says, he has no borders between thoughts, so I suppose that Will needs very fine control, or at least need a sense of having control — confidence in his self — to work. This does not mean that Will is one step away from becoming a murderer. This means that Will is one step away from having a breakdown over whether or not he still has control. This doesn’t make him less capable, it makes him vulnerable. He needs his own borders where he knows where everything is inside his head (his room, for example, perhaps a physical manifestation of this if I’m being pessimistic (and I’m sure someone can come up with a more optismistic explanationn for it as well, all about perspective)) so when he tells Hannibal that he feels as though someone moved around the furniture inside his mind, he is saying he is losing confidence within himself.

Later, when he finds out that it was Hannibal’s manipulations that have led him astray, he acts with self-possession. He is alert because he has figured it out. He is confident. Angry. He is back with vigour. Perhaps this is worse because while he wasn’t conscious during the first ride, he now willingly gets into the rollar coaster with Hannibal in order to catch him.