Madotsuki is the main character in Yume Nikki. Fans speculate that she is young, anywhere from nine to fourteen years old, although arguments can be made for any age. One notable argument is that she is "chibi" style and probably no younger than 16 if she lives alone.
Not much is known about this girl, and only what can be seen in-game can be considered canon.
Madotsuki doesn't have much to do in her room. Her TV doesn't receive any channels, so she can only play her single game, Nasu. She can go outside on the balcony, but the balcony itself must be rather high, and her view always seems to be blocked by fog.
She seems to be a hikikomori, or shut-in. This is supported by her refusal to leave her room- instead, she simply shakes her head. It is possible she is depressed, and the dreams are caused by her medication. (REM rebound, common for low dosages and withdrawal, or longer REM cycles.)