when I was a young teen my other use to take me to Freud clones, and two of them fell asleep on me. I never said a word to them. When they woke up they would call my mom in and tell her I wouldn't talk. As soon as I got in the car, she would start to kvetching.

If it happened now I would probably tolerate it once or twice with some explanation, but if it continued to happen I would exit. I would also ask to be compensated with a free session when it happens, because it's a business deal.