I think RedRiverTears put it forward perfectly. You probably won't be able to dream while under the heaviest portion of the anastesia,(no idea how to spell that lovely word) but afterwords, when your laying in the recovery room you may have some dreams, trippy as someone above said since you'll still be under the effects of all the painkillers...either that or you'll drift into a dreamless sleep afterwords...but I remember feeling very dreamy and strange in the recovery room. Maybe that would be an opportune time to play around with the drugs effects since you're no longer under the knife .

Anyway, it wil lcertainly go fine...in fact it can be quite fun with everything the plop into your system.