I've searched for this fic once before but didn't get any results a few years ago, and it's sprung to my mind again and is now driving me crazy trying to find it so I figured I'd try again. This is definitely an older fic (I'm thinking probably around 2007/8) and is longer one...

I'm not 100% sure if it's a curse or a spell but Sam gets either sent back in time or to an alternate universe where there is another Dean and Sam - the two Sams swap consciousness but still retain their own appearances. In the past/alternate universe, Dean thinks Sam is insane as he is speaking of a different Dean and the future and possibly demons so he sends him to an asylum where he is very much mistreated. He's kept in isolation and chains practically 24/7.

I remember two specific scenes where he is being bathed/tortured, and another where Dean goes to visit him and he is very withdrawn and gaunt, and his hands are covered with a shawl to hide the chains/bruising. He begs Dean to take him home and Dean sees the chains, but he is convinced that his brother is violent which is why he needs the chains... Sam ends up escaping or being rescued by Bobby, and cared for by Jess who is Bobbys daughter... In the present time Dean and Sam from the past try to work out what happened and break the spell/curse to return them to their own timelines...

If anyone knows this specific fic it would be very much appreciated! I'd also like some recommendations along these types of stories & themes.

Thanks!