Well that was perturbing

 I'm doing slightly better with sleeping this week, but still sleep-deprived to the point of being a shambling bundle of "SLEEP NOW!" when it catches up with me. So I'm not quite sure if this happened on going to bed (9PM-ish), in the middle of the night, or when I woke up at c4AM.

Whenever it was, I needed to go to the bathroom. My bed to the door of the bedroom is two to three paces, as I got to the door, my right knee collapsed under me. Not went a bit floppy, there was zero support from that leg, so I went down sideways like I'd tried to put weight on a leg that wasn't there anymore. I grabbed the doorpost with my right arm, and I must have been falling backwards, which turned it into a swing around through a whole 180 degrees towards the bookcase that's just inside the doorway.

I had time to think "This is going to hurt", and I was right, I took the edge of a bookshelf across both kidneys, I won't be surprised to find a bruise there, and I hit hard enough I was worried I was going to bring the whole thing down atop of me. Fortunately/unfortunately the thing is incredibly heavy, so didn't move, but nor was there any give in it.

Let's just say I sat there for several minutes before I could think of moving. I vaguely remember crawling through to the bathroom, I presume I crawled back to bed.

And this morning my bloody right knee is working fine. "Wot? Who? Me, guv? You got the wrong fella!".

I've paced it out, I have to have taken at least one pace on my right leg before it collapsed on the second one. Why?!?