My only excuse is that I was still barely awake and it was quite dark, but I somehow managed to completely miss the last stair and stepped out into the hall that was much lower than it should have been. I did a rather spectacular left bum cheek, left knee, right shoulder then face plant, but at least a rolling impact with the floor means nothing is damaged beyond a bit of bruising.
I've lived in this house for 11 years, I really ought have some sort of internalised count of the stairs. I much prefer flat living and have been talking about moving to a flat once the DC are older, might need to bring that plan forward a bit. 