Looks like you'll need some gyros. Anything with gyros will be expensive, and will involve some complicated math. The cheapest thing off the shelf I know that will do this is this:http://www.aeropix.ch/store/index.php?main_page=product_info&cPath=2&products_id=8&zenid=0946a83e267a29cce654240098a4dd37
It will interface with a radio control airplane transmitter, but I'm not sure if it'll be easy to interface it with arduino.
If all you want is tilt, you can use an accelerometer, which are much cheaper and easier to work with, as long as the person doesn't move around too much. You can also use a magnetometer (electronic compass) to measure pan angle, but they are hopeless when the tilt angles gets large. There are 3 axis magnetometers with tilt compensation and fancy stuff that will work, but they are almost as expensive as a full gyro solution.
Trying to find the attitude of something in space is tough, maybe instead of a full inertial measurement unit with gyros and stuff, since it's inside a room, you can consider using a camera and some IR LEDs on the person's head and do image processing. I think that's how the Wii controller works.
If you find some better solution, let me know. I'm also trying to figure out how to do this cheaply.