Once, for just long enough to say, "son of a ..." and then I was out of it that quickly.
I was running a buddy over to another airport so he could pick up his truck. He'd moved his airplane and needed a ride back to get the rest of his stuff.
It was low overcast, but not bad at all. I'm pretty conservative on clg and this was low but not too low to be a bother. The problem was it was a really gray day, and not a really well defined clg, it was pretty ragged. I was starting to descend to TPA and a small line of low clouds was hanging below the rest. They were invisible against the background. I was looking down to get a good visual on the airport when everything turned gray. I never saw it coming, everything just blinked out. I got onto the instruments quickly, knowing that I'd be through it in just a few seconds anyway. My goal was "don't make any sudden moves". Sure enough, I was back in the clear and everything was fine. We both thought to ourselves, we shall never speak of this, but it was a good lesson for both of us. Neither one of us could see those lower clouds that day.