My Cats Keep Following Me Into The Bathroom

I'm usually alone at my place, so I don't always get into the habbit of shutting my doors completely when I go from room to room. But one thing in particular that has been kind of creeping me out is that my cats keep coming into the bathroom with me and won't leave me alone when I'm in there.

Is this a normal thing?

I know that cats like to mark their surroundings and all, but what is their fascination with me? They start acting like I gave them catnip or something.