The poem turns the speaker's mouth into a theater, a place meant for performance, and then says the first play staged there was one the speaker never saw. That odd detail suggests words that came out before the speaker was really aware of them, speech that happened without being watched or understood. The title, "Talk therapy," hints that talking is the subject: what it means to speak, and what it costs.
The feeling is tired and numb. The speaker was "weary" of that first play almost immediately, and calls it "so dead" that sleep became impossible. The image is a little paradoxical, since boredom and deadness usually make us drowsy, but here they keep the speaker awake. Judging by the imagery, talking has become empty ritual rather than relief.
The mood is quiet, dry, and restless. Short lines and abrupt breaks make the poem feel halting, like someone searching for words and not trusting the ones they find.