Well Poppy,
I would respect the workings of the universe and not fight against them (you wont win). Perhaps now is not the time? Perhaps your friend has picked up a 'vibe' which has frightened him or disconcerted him and he needs to take a 'time out'. This is all perfectly OK and very understandable.
It's dark apart from some fire light...I see him ... he is on his knees and struggling to get up...his hands are tied behind his back, there is a large piece of wood tied too which is weighing him down...
This is all fairly scary stuff, after all. As I said, most people don't have these memories in their conscious awareness, but they are right there in the unconscious (whatever that is). His seeing you may have stirred up some feelings of things being 'not right' even though he may not understand why.
I would just go easy for the moment and see what happens next. Just keep it lighthearted if you do run into him again, and don't mention any of this stuff for the time being. It will only frighten him away more. Just talk about the weather or the football or something, so he gets to know that you are not a mad person and are not frightening or anything and mean him no harm.
You have all eternity, after all.
Meanwhile, if you just can't leave it alone I would try writing out the whole story in long hand. If you are not sure of a detail, close your eyes, take a few deep breaths and just write the first thing that comes. It has a way of being the thing you are looking for. Pretend you are just making up a story for fun and see what comes out of that.