Going blank is a different machine

The loop above explains not starting. It does not explain the other problem, so here is that one briefly, and lesson six takes it properly.

Test anxiety has two parts and they behave differently. There is the body part, the heart and the nausea and the shaking hands. And there is the thinking part, the running commentary about how badly this is going and what it will mean.

It is the thinking part that carries the damage, and the reason is mechanical rather than mysterious. Working memory is small. If a good share of it is occupied by monitoring how you are doing, there is less of it left for the question in front of you. That is how somebody who genuinely knew the material can lose marks on it.