I haven't seen this, but I have heard of it, and I did get into trouble once with a sub who got so deep into role-playing a kidnap victim that she forgot she had a safeword.Another good reason to play with people you know! The sub mentioned above was one I'd only played with once before, if I'd known her reactions better I wouldn't have missed it.I was too far out/ down/under, where ever it was, and all I could mumble was "help, help, help" and he realized I was serious and quickly released me.
My late wife didn't have an official safeword - we started with one, being responsible players, but it was a big moment in our relationship when I took it away - but if she called me by my name instead of "Master," I knew it was an emergency.