Hi boef f,
Welcome!
Jhana is about specific concentration states while A&P refers to a developmental landmark. Increased access to jhana or other concentration attainments can be an indicator of A&P developmental "territory", but there are many more.
Have you tried a formal resolve to enter that state again? Once you get good at entering it, you can find out more about it.
Retreat: well, if it's a guided retreat with a teacher, follow the instructions of the teacher. It would be a shame for all of you, students and teacher, to make the effort of attending that retreat only to do something completely different. If it's a solitary thing, maybe you'll find Tarin's
Reformed Slacker's Guide useful.
Cheers,
Florian