Two days. That is the gap after a first session when a patient has had time to feel the effect and has not yet decided whether to come back.
At 10:00 on day two a text goes out from the practice number. How are you feeling after Tuesday. One line, a rebooking link underneath, nothing else. If they reply, you see it. If they book, the diary fills.
Six weeks after the last appointment in a course, a second message. A check-in, a softer tone, the practitioner's name on it. Some people are fine and say so. Some have let it slide and were waiting for a reason.
Then the long tail. Anyone who has not been in for a year and never finished their course gets picked out, and a short personal note is drafted for you in Gmail or Outlook. The draft sits there until you read it, change a word and press send, or delete it because you remember why they stopped coming.
Replies that mention pain, a worsening, or a question about what to do next go to you as written. The system sends messages. It does not answer them.
This is the kind of thing we build. It runs in your own accounts. How many patients from last January have you heard from since?