Yeah. I think we've all been there somewhere along the way. In the past, I referred to it as "writing myself into the corner". It came from not having a clear end goal. I don't get that quite so much now. It's part of the joy of having a basic outline.
No, now I suffer from burnouts. I blame this on writing so fast that I get ahead of myself. Either the characters stop talking first or the background'll fade, leaving me with dialogue and breaks full of [???].
To clear my head, I take a deliberate step back from the writing. Perhaps I'll play a computer game or watch TV or work on something else ... basically anything that get me away from that story. Often, the storyline creeps back into my brain like an ignored puppy pawing at my leg for attention.
What do you do to get rid of a case of "Uh..."?