You used to know but now you've forgotten/A submarine got stuck to the bottom

I love the Lightning Seeds and have been listening to them all morning because they invariably make me think of spring and summer, but I have never quite managed to understand what exactly this lyric is getting at.

Gah. I hate having to work on bank holidays. Thursday afternoon they brief me that they need a case summary in a heinously complex fraud case to be filed in the High Court by 4PM on Wednesday. No one has written it, and since I'm the cheapest barrister who has previously worked on the case, would I mind having a copy on everyone else's desk by close of play on Tuesday...