名前をすっかり忘れてしまいました。

name; full name; given name; first name

indicates direct object of action; indicates subject of causative expression; indicates an area traversed; indicates time (period) over which action takes place; indicates point of departure or separation of action; indicates object of desire, like, hate, etc.

all; completely; thoroughly

to forget; to leave carelessly; to be forgetful of; to forget about; to forget (an article)