I went up to his room with the intention of sleeping the rest of the night in there, on the floor. I somehow knew that would be necessary. When I got to his room, he was kneeling on his bed, peering over the toddler rail, staring at the place I had laid, and crying "mommy, mommy, mommy."
I had disappeared in the night, and he was scared.
That's my fault. I had not made clear the expectations. Tonight, and every night, we will tell him that Mom (or Dad) will stay for a little while, until he sleeps, and then go to bed downstairs. He's smart enough to get that, I think. He may not like it, initially, but it'll save my back and hip....hopefully. That nursery room floor is awfully hard.