Been there, done that!
Back in my teaching days, shortly after returning from a conference in Adelaide, I nipped out of my classroom to get something from the stockroom. When I got there, I realised that
(a) I'd no idea what I'd gone there for ;
(b) I'd no idea which class I was in the middle of teaching ;
(c) I'd no idea as to which topic I was teaching them ; and
(d) I'd no idea as to which classroom they were in.
I had to wander down the corridor, looking through each door, to find a class that hadn't got a teacher and then look at their exercise books to work out what it was that I was meant to be teaching them!
That was 36 years ago and I've not totally lost my marbles yet ;-)