LostSoul
Adventurer
I think it might work out okay if you tell the PCs that they have obviously been through torture - they have this general impression of unbearable pain and degredation - but they can't remember any of it. Then you get the chance to use the torture session whenever you want as a plot device, not just something to freak out the players.
The first thing that springs to mind for me is a invasive parasitic fungus that slowly transforms the PC into a fungus-guy. Over the weeks and months, he notices strange changes coming over him - pain here and there, fragile bones, thick, sooty urine, fungus growing and spreading over the skin, mushroom-like flutes appearing in his throat/under his arms/between the legs, etc. This kind of disease has a parallel to many real diseases (such as cancer), so any player sensitive to a slow, wasting disease could be hit hard by it.
The first thing that springs to mind for me is a invasive parasitic fungus that slowly transforms the PC into a fungus-guy. Over the weeks and months, he notices strange changes coming over him - pain here and there, fragile bones, thick, sooty urine, fungus growing and spreading over the skin, mushroom-like flutes appearing in his throat/under his arms/between the legs, etc. This kind of disease has a parallel to many real diseases (such as cancer), so any player sensitive to a slow, wasting disease could be hit hard by it.