I know the feeling but I think I've (mostly) got to grips with it now. I'm not sure whether it was on the lens or on the camera that you switched the AF off but it seems to me that Nikon has a design fault (yes, just the one
) in that every time I take my camera out of the bag, the focus selection switch has moved back to manual. The first photo is usually out but then I remember and check the position, move it back to S and then when I half press I hear the beep.
The switch on the lens is a different matter but the rule still applies: if it doesn't beep it's not set right.