I am installing a ceiling fan in a bedroom. right now there is nothing in the ceiling so I'll add a fan box up there then run wiring across the attic. My problem is that at the bedroom door there is a switch but it controls an outlet on the far side of the room, probably for a bed lamp. So, my question is if iI want to add a new switch next to the existing one, how do I get power to it? The existing switch has only one cable in the box so it is a switched switch (?)

Thnaks