It sounds like the air is just too dry. Hard to come up with a humidity number, but I don't think it would be really happy with the humidity below 50% - that's just a guess though.
Best bet is misting it a few times a day or sit it on a tray of pebbles sitting in water like Elaine said. Better yet, if your bathroom is big enough, it would probably enjoy being in there whilst you're taking a shower, but don't leave it in there unless you have a window in the bath.
