LOL .. maybe it's just me, but the other night I had an epiphany!
I was mucking about with the D800 and had set it to ISOHi1 and Hi2 for some tests I was doing. Just mucking about, as I'm unfit for photography at the moment.
Anyhow, because I manually set the camera to ISO so much higher than normal, and only mucking about, I forgot to set it back to ISO lowest base value + Auto ISO set to on(for the next time I try to use it seriously).
At about 1AM one morning(maybe Sunday night) I suddenly woke up from a land of Pentax 645z and some far distant exotic location(yep! dream world) and rushed back into my office and remembered to set the D800 back to my preferred base ISO + Auto ISO on.
I don't reckon I have the cranial capacity to remember to do that if I was out taking serious photos .. but for some reason during a nice warm slumber I did.
You should have titled the thread ..
Check your camera settings ... during normal hours!
And damn!! ... it was cold that morning too!