Dock somtimes disappears but comes back

Has this happened to anyone else?

Sometimes when I'm working, depending on the keystrokes I use (I think, though I haven't been paying attention, when I'm cmd+tab'ing to switch between applications), the dock will momentarily disappear, then reappear, 'rising' into place, like it does when you first turn on the machine. It's a new phenomenon. Can anyone tell me if this is a problem, and is it possible to fix?

Option Command D are the quick keys to turn Dock hiding on and off if that helps.

To me, it just sounds like you have the dock hiding function turned on. I wouldn't know though, simply because I'm not you

The option wasn't turned on -- so it's something else. anyone out there have any ideas?