The first time I did salvia, it was during a nitrous session. I'd probably hit four or five whippets before smoking the salvia, but it ended up awful nonetheless. I think I smoked too much of the salvia (about .75g of the 20x stuff in one hit), it was the most difficult time I've had with salvia and none of my future salvia attempts were anywhere close to this combination.
I remember loading the bowl, hitting another whippet, then I remember lighting the bowl and that's when all hell broke lose. I don't remember inhaling the smoke or blowing it out, I was just instantly 'sucked' into my monitor, chopped up and torn apart by huge gears, then launched out of the monitor hitting the floor like melted cheese. I remember 'pulling' myself up from the ground while hearing some sick circus/carnival-like music playing to a marching beat, I remember seeing a really big wheel turning that very closely resembled the Wheel of Fortune wheel, then some kind of huge grocery-store sign was 'pulled across my face'. I also remember a very physically painful situation that involved being pulled through a never ending row of turnstiles. I somehow managed to run outside, then this ordeal started dissipating.
I'm not exactly sure how the nitrous played part in this deal, but I'd like to say that it somewhat potentiated the experience. It was certainly an eye-opening event, but the physical pain and distress that I felt during it made it not something I wanted to immediately try again. I'm not sure how 'real' the pains were, but at the time, they sure did seem very real. Surely the nitrous did not 'take the edge off' of the salvia experience, but it definitely made it more vivid and sick than the other times I've done salvia. I'd say be careful and expect the worst likely event to occur.