I don't know what his nightmare was about, but whatever it was, it gripped him hard.
Poor dog was thrashing around, not just the twitching paws but his body flailing around, growling, biting at the air, it was intense. Took several minutes just to wake him from it, and when he did, he wasn't aware of anything in terms of where he was or who I was - even growling at me while I was holding him.
He settled down a little bit and started to recognize where he was and who I was, but he was still terrified. I set him down and gave him some room as he was panting very hard and visibly shaken up. He started looking at me as I moved, but he still didn't want to get up. When he did, he wanted to go hide in his other spot in my room.
Whatever it was scared him so much he had peed on himself and he had an accident trying to get outside. Still scared and skittish, but moving around and following me a bit. I took him out for some air and to let him just clear his head. The walk eventually started settling him down and he got back to his usual self more.
While outside, just wanted him to get back to his usual self and we played some and such. He started relaxing and shaking his body (calming signal, usually a "whew, that was intense" or "glad that's over" type signal) and quickly started coming around to himself again.
I hope he doesn't have to go through that again, though I guess if it happens again, I know what to do to help him out of it and settle his mind.