I am getting nauseated every time we watch something in the theater room. I think it is because the picture is too large for the room. What is the rule of thumb for screen size to room size? Any other suggestions appreciated!
While you have received several good ideas, one of the things you may want to do is to ensure that the room itself doesn't have any issues that are environmental. Spend a few hours in the room playing a game or reading a book and see if the nausea kicks in then as well.
I found in my new home that we had a minor gas leak in the basement which would affect people if they were in the basement for hours at a time. Under an hour or so, no issue, but over an hour? People would feel headaches and get dizzy.
Any number of things could cause the issue.
Now, if you find no issue, you can test the screen size by zooming the projector in so it fills less of the screen. This should be very easy to do and takes only a few minutes.
Also, a cheap DLP projector of a business class, may only have a 2x color wheel and you could have some issues with this.