I turned my cellphone on in a dark room and the light from it caused me to lose my balance and i almost fell backwards, what could cause this?

Your brain uses inputs from your vision to make minor adjustments in balance continuously. These inputs require some light to function. In a dark room setting you can easily be off balance from the lack of these adjustments. I can easily see where the inconsistent and abrupt change in lighting could throw you balance off in that setting. If this happens a lot, go see your doc.