Fuck that... better not to get involved IMO.It appears that what must be done when somebody goes off the rails on psychs is to actually tie them to a chair until it's over. If they're loose at all they'll do something insane and possibly hurt themselves or others. Just keep some rope on hand for such occasions and a good sturdy chair. Or I suppose you could hogtie them on the floor, but they might squirm around and bang into stuff. If they get mad about it later and start talking shit about having you charged with false imprisonment or something just remind them that it's their word against yours and they're clearly deranged so who will the cops believe?
I once had a paranoid schizophrenic fuck out on me on his first acid trip (I was unaware of his condition when I dropped with him).
I was tripping on 300mcg and holding back the urge to beat the piss out of this obnoxious and ungrateful motherfucker. I cussed him out and left him on his own (we were tripping round his flat). He got committed and from what I've heard he's still in hospital a year later.
By all means try to talk your friend out of a bad trip, but you have to respect your own well-being. If they start fucking out big time and won't listen to reason or let you relax then the best thing to do is leave them alone or kick them out (if they're tripping round your house).