I know that I used to have this problem when working with higher ranked students. It mostly came down to figuring out "if I resist, this really hurts!" and not being able to stay relaxed and extended at the same time. With a choice between resisting and dead, I was choosing dead as it was less painful. Luckily, I figured it out on my own through the course of practice (kinda) and can now try and deck someone and still survive all the way through the pin/fall.
If the student is trying to attack sincerely, she/he will get there eventually. If the student is doing it on purpose after being talked to by the sensei, and in doing so impairing the ability for other students to learn, the sensei will take care of it. Until then, consider it training for when someone blown out of their mind "attacks" you in slow motion and in a completely unbalanced way. ;^)