I simply can't believe what I am reading.
From whatever cause the airframe gets so badly trimmed that it goes into a slow speed fast sink condition.
We are calmly told that the way out is to apply a total of ten seconds full nose down before any beneficial effect is seen.
Not exactly intuitive, and unlikely to be discovered amongst all the other similarly improbable actions.
The aircraft simply should not permit this to happen. There is no justification for the THS to move so far so quickly. If it had been rate limited, at an appropriately slow rate, it would not have put the airframe in such an impossible state.
Or can anyone think of a reason why the autotrim would have to respond so dramatically in steady high altitude cruise?