The question is not, is it normal, but does it work for you? If it does, it's cool.

My ex-slave more or less panicked when I once mentioned the possibility of my switching: the idea of her Master submitting to someone else made her feel like the ground was giving way. But plenty of people aren't that set in their views.

For anyone new to the scene and wanting to get a taste of the sheer variety of possibilities, I strongly recommend Antoniou's "Marketplace" series. The hero is a slave trainer - powerful Dominant and brutal sadist - whose tragedy for the first few books is that he needs to be owned and can't find a Dom to take him. You might jump in with the later "The Reunion" where he has both a strict Master and a devoted slave.