He pops his eyes open, starts kicking his legs, and starts wriggling his arms (in the swaddle). Most of the time, I have to give the pacifier back to him to get him to relax again, but today, on 2 occasions, I was able just to pat/shh (yea!, progress!).
I'll watch for a triggering event, but at this point nothing stick out. He will seem completely relaxed and asleep, then his eyes just pop open.