Dreaming of sleeping under your bed means you are in a relatively safe place. This type of dream can be triggered when you had thoughts of anxiety, security and well-being, during your daytime.
There is a myth about monsters hiding under a bed. This legend resulted from childhood fears of the dark, and unknown. It is generally dark under the bed, especially at night. Besides the dark, there might be cobwebs and spiders under the bed. While the dark and scary may be under the bed, this place is also a safe place as no human would think of hiding under the bed, or looking under the bed to find you.
If you dream of sleeping under your bed, the dream interpretation is that you were looking for a safe hiding spot.