I don't have any experience with LSD/LSA, but I think the risk here is in tripping without a sitter. He could 'forget' about his condition, try to walk/stand up and fall.
Furthermore, when taking substances that cause nausea (mushrooms, for instance) vomiting could be severe issue for him, unless he sets up a room with a basin, towels, water and everything he could need.
I've had a bad trip with DXM (it is up to you to decide whether dissociatives are or not psychedelics), and i spent hours crawling to the bathroom to vomit, then climbing back up on the bed, crawling again to the bathroom... I cannot imagine how that would have ended if I did not have even the little mobility that remained.