I am assuming you mean the "illusion" of pain, as referred to by Steely ^^^^^. While I haven't experienced physical pain myself (although intense pharmacologically induced psychological/spiritual/noumenal pain is perhaps indistinguishable from physical pain), I recall reading a salvia report on this site that really struck a cord.
This particular salvia smoker was propulsed into a world that was essentially an infinite field of coke cans - and he himself was one of these Coke cans!! (I know, I know... first the middle east, now the Coca-Cola company has tapped into the far reaches, the very antipodes of the mind to advertise!! Have they struck a deal with lady salvia?:lol: )
In his description, the coke cans were being crushed by, if I recall, huge plungers jetting in from above, and every once in a while it was his turn to be crushed. He described feeling intense pain, as if it were really happening, feeling the bones collapse and crush within him. Moments later he would uncrumple and become a fully formed can again! Only to await the next crushing in dread. Having no recollection of ever having been anything other than a can, he also felt that this is what he would be eternally - a coke can in a field of crushing coke cans!! If I recall as well, he was that can of coke for 1 full week before coming back to his body... (I apologize to whoever this was if I am in error regarding some of the details. It was a trip report that really struck a chord with me - not the same as my trips, but I think anyone who has gone deep with salvia will be able to to identify, and even imagine this happening to them...)
Salvia is STRANGE stuff indeed. Particularly if it allows you to experience, in addition to the anguish of forgetting who you are and becoming an object, true pain, or an illusion so complete that it is indistinguishable from true pain.
I know of others who have experienced physical pain after smoking significant quantities of salvia, but not from any other substance. Here's a question though - is it really physical pain if there is no external, physical phenomena causing it?
JBArk