Update: therapist brought up the couch again. I've been having some intense trouble talking the past two sessions, about a difficult topic that recently came into focus, and he still thinks lying down might help. So I said I'd been thinking about it, and that given how things are going I'd be willing to try it.

He was really reassuring about how flexible it could be--that he could sit in sight of the couch or behind it, that I could feel free to alternate between sitting up and lying down as much as I wanted, etc. So I'm going to at least try to try it next session even though it still seems strange, and I guess we'll see what happens.