This happened to me in the bathroom the other day. I forgot how to pull my pants back on! I was just staring down, wondering...how do I do this?
I don't really need to be tired. Entirely random, usually it will be when in the mental world and then forced to respond to something environmental, like putting your pants on, where the "handoff" gets tripped up.
That happened to me once. I forgot how to put my sweater back on. True story.
Washing my hair twice, missing freeway exits, wearing underwear inside out, wearing pants backwards, sitting or standing and staring into space, almost brushed my teeth with face wash but I caught myself (ha!)
Also the "what was I doing?" and "How do I do this?" moments as well as forgetting certain things I studied/crammed the night before in the middle of a test.
The "how do I do this" part was me explaining afterwards what it seemed like. During the actual horrifying experience, there was just nothing. No mental activity whatsoever, I was completely lost.
Get that. For me it links into what I was talking about in this thread about not thinking conscious thoughts. I'll be so tuned out that it'll take me a moment or two before I can comprehend what someone is telling me. It's like I'm here but my brain has gone bye-bye.
I get this more times than is probably normal, and it is a terrifying experience each time!
Sometimes, I'll just sit there willing my brain "to turn back on" or I won't even notice that I've "spaced out".
I've also had the experience of forgetting how to put clothes on, though in my instance it was tying my shoes.
I have a sort of similar thing where sometimes I'll be doing something mindless but still requires enough mental concentration that I can't completely drift off to think about other things and I'll find that my brain will just start jabbering, often mildly offensive and suddenly I'll reengage with my thinking process and go "what?"