In college, I was doing a two-man Black Box play (Arthur Miller's CLARA) with a good friend of mine. We were about 20 minutes in--and mind you this whole play is essentially an interrogation/recollection piece--when we slowly started to realize that we had skipped about 20 pages ahead in the script. To this day we still have no idea who gave the wrong cue or how we got off course, but SOMEHOW we managed to talk ourselves back to where we needed to be without anyone in the audience realizing it after the fact. Horrifying and exhilarating.