phrases - "Only when..." vs "it was only when..."

In the following example:

Eri stared at date on the screen, but all she saw were white pixels.
Only when she recovered from her shock that she became aware of its
meaning.

Do it have to add "it was" before "...only when..."? Or it's not necessary? When to use only when and when to use it was only when?

Answer

You have to say either

It was only when she recovered from her shock that she became aware of
its meaning.

or

Only when she recovered from her shock did she become aware of its
meaning.