The link you gave describes three types of freezing. "Tonic" is the 3rd kind it describes and it is the most extreme case:

When one’s body perceives that death may be impending and fleeing the situation is not an option

The article's sources hypothesize that the body goes into this state only when it cannot flee or fight:

Finally, if the body’s limbic system observes that there is not enough time and strength to “fight” or “flee,” then the body will induce a freeze response (Rothschild, 2001, p. 10).

When you're climbing near your limit, you are in a place where you cannot flee, there is nothing to fight and "death may be impending". So the fact that you're worried about Tonic Immobility is reasonable (I also like the fact that you're taking precautions in case this happens -- good for you). I would most certainly understand if this reaction took place with a person was violently raped by known or unknown assailants. I do not however believe this type of freezing occurred in the situation I described based on the tidbits in the article (which shouldn't be taken seriously, honestly, because it is no more than an educated guess).

A disturbing thought formed: What if he doesn't know what he's done?

I seriously cannot fathom an adult not be able to understand that the person you're in the same room and you're having sex with is in fear of her life because of you and the things you're doing; to a point that you would brag about it afterwards. And I also seriously cannot fathom a person in the United States that feared for her life to a point of having an extreme subconscious reaction would not go to the authorities let alone the university to report the incident that caused her extreme fear. At a minimum once the 'flee' option was available, I'd argue that a person would flee from the environment to be far away from the cause of that extreme fear (i.e. she would have stopped going to University).