Mario was sleeping, because he had nothing to do. No imaginations, no weird or awesome dreams, just sleep. And why? Because he was absolutely bored of his mind. The red capped plumber could have used a nice blank break for quite a while. Things were going very pleasant for Mario.
Until Bowser and Waluigi bombarded the house and stole all of Mario's fifty cookies. Yes, Bowser and Waluigi just stole fifty cookies from Mario. That's ten cookies by five.
And that's terrible.