The castle suite is the most obvious choice, but if you were "trapped" inside the MK I hardly think that area would be accessible. It's kept under lock and key day and night.
SO, I would say the Swiss Family Treehouse. Or perhaps inside a Dumbo, a teacup, or a TTA vehicle. Maybe I would set up camp in the Rose Garden. Would love to sleep somewhere on Tom Sawyer Island but I'm not sure how I would get over there if the rafts weren't running.