"Why didn't he tell her what had happened?" "He had fallen on the floor"

Question

Sometimes I am not sure whether or not I need to use the past perfect or leave it out completely.

Why didn't he tell her what had happened?
Why didn't he tell her what happened? (Are both of these sentences correct)

He had fallen on the floor and then went to hospital as he had an injury.
He fell on the floor and then went to hospital as he had an injury.

I assume the first one suggests that it had taken some time for him to make his way to the hospital after falling, whereas the second one suggests that the it all happened quite fast.

Answer 1

All of these are correct, and each pair can be used essentially interchangeably. The past perfect (that is, the "had" form) emphasizes the process by which the current state of things came to be, and may imply that the events are not quite recent, but that implication cannot be trusted. The simple past form emphasizes the current (resulting) state more. Nothing can be conclusively determined from which form is used.