As 12 seems to be the limit except in exceptional circumstances, I just prioritised what I wanted to address and tried to be as positive as I could about the last session.
I remember my last session as having a similar feel to that last day at school before the xmas break; the day when everyone was allowed to wear whatever they wanted and very little, if any, classwork was done. Very casual and very end like and strangely liberating as it was very obvious both he and I could see the difference in my whole being.
However, compare that with the previous ending (which felt quite rushed and incomplete) and in a similar way to you I managed to unravel a particularly deep-seated problem in the penultimate sesh that left me quite shocked. The therapist was a little concerned, if all be told, and suggested I be around other people for the following week. It was bad timing but something very significant in helping me sort things.
I was worried I was suffering some sort of dependency issue when I felt lost but it turned out I had triggered something that needed sorting and in a therapeutic environment as opposed to one’s own headspace, which can sometimes have limitations with certain ‘issues’ IMO.
Obviously give the light thing a bash – most of the advice on this thread has merit. But as Jambalaya suggests, it has to be worth a trying to get a few extra sessions with the guy, though I’m unsure whether or not they’re allowed to offer their services outside of the agency. You might get lucky as I did.