Setting offset regarding post being viewed ?

Hey guys.

I’m trying to set an offset regarding the post currently being viewed.

For example if the user is Viewing post 10 I want to set an offset so that the posts showing in the sidebar will be

post 9
post 8
post 7

And if he clicks on post 8 it will then show:

post 7
post 6
post 5

I’ve already tried a lot of stuff but nothing worked. Does anyone knows how to achieve this effect? Thanks!