すっかり忘れていた.
We forgot.
I forgot.
I forgot all about it before I knew.
I remembered.
I forgot all about it in my joy.
お忘れなく
to forget oneself―lose oneself (in admiration)―be lost (in admiration)―be absorbed (in study)―be engrossed (in one's business)―be beside oneself (with joy or grief)
That reminds me of something.