Sit down and go through the recent incidences to see if there could be any merit in it, who knows, he could be right and you can help him tackle them. What kind of things is he talking about?
Even if it is real it could knock him and set off his illness again so to have the relevant back up will help.
PS is a lifelong condition, it not cured but can be controlled. Has he shown any other changes in behaviour of self care?
An appointment with his consultant, or gp in the meantime, could be a good idea as he may need a check up, adjustment of medication or further assessment or treatment just to make sure he's receiving the most appropriate help for him. Is he on any medication, if so is he taking it properly and how long ago was he last reviewed? Could he be taking anything which could be interfering with his medication?
Never underestimate the cruelness of some people, whether they know about his past or not it horrifies me what some people see as amusement, revenge or whatever.
Try these for some further advice...
http://www.sagb.co.uk/
http://www.sane.org.uk/
http://www.nsfoundation.org/sa/index.html
http://www.world-schizophrenia.org/