Would you send one for turning up to a session with a very low mood? Not for having a low mood, but for how it affected the session. How it made the therapist feel stuck with helping you move on. How it opened up important information about you, which you, when it got so close to explaining/clarifying so much, blocked it out, blocked T out. As you always do, regardless of how well they understand. I’d find that difficult as a T, which I know doesn’t mean others would, but they could. And most don't want to make things difficult for others.

If not an apology, would you text anything else? (Baring in mind that this T has said you should text if anything pops up following a session like this)