Running out of dreams

Sometimes (rarely) Z will have a nightmare and require a few minutes of comforting. The other night, a call from the son, and a prod from the wife and I stumbled to his room, trying to move from irritated woken sleeper to comforting father.

Me: Hey sweetie, had a nightmare?
Z: No, I had three good dreams, but they woke me up.
Me: Why did you call out, then?
Z: I didn't have any more dreams to go to sleep with.