Two things I think are very important here. A safeword (as this will tell your Master when he HAS reached your limit). And, your own research. I know, this is going to sound strange but it is like going to the doctor. Some people go to the doctor without doing any research themselves and can be misdiagnosed and also misprescribed. You need to care about yourself enough to do your homework. (Not just in this case but in all cases.) First off, buy an anatomy book, find out where all your sensitive spots are (like, your main arteries, and your vital organs) and make sure he avoids these areas for any extreme play. For instance, some people don't realize to watch out for kidneys (the lower back just before the ass cheeks) when doing a whipping or a beating. It could cause damage in extreme (and even not so extreme) time, even though you see it done quite a bit. Because I did my research, if a Master went there, I would quickly use the safeword. There are many other places to beat (twice as hard and twice as long), he doesn't need to use that one and put my health at risk. But, if you didn't do your research you wouldn't know that it is vital to watch someone that goes there and that it is not a sign of weakness to use the safeword if someone goes there. So, again, I would suggest, do your research and then if you want I think it is a perfectly "okay" fantasy if you keep your safeword handy so that when you DO find out your limits you can define them appropriately. Your body DOES know when it has had enough (usually) and your actions and voice need to reflect that and your Master/Dom needs to respect that that. The fact that you desire "no limits" is a good fantasy but realisticly speaking the Dom/Master does need to have SOME guage (like the safeword) for his sake as well as your own.