Sounds as though he may be having an Allergic reaction to Opiate-based pain meds or possibly too Strong a dose,hence possible Hallucinations,Also it is quite common for many folks to Scratch themselves,for the feeling of something crawling on or under your skin,or tingling nerve sensations,Mainly from Opiate-based pain meds.Talk with your sis to see if they can change his pain med to Non-opiate based such as Demerol & observe the difference,if any!Good Luck with This!