Well, you can! With a little prep before you hit the pillow, you can actually make slept-on hair look good...
Start by shampooing before bed, and then try one of these tricks:
1. Waves: Apply a styling cream from roots to tips. Comb your hair into a tight bun at the nape of your neck, and secure it with an elastic. When you wake up, remove the elastic and run your fingers through to separate the waves.
2. Beachy Texture: Work a product like styling lotion through your hair from roots to ends. Part your hair down the centre, and create two loose braids starting above your ears. In the morning, undo the braids, and spray in some texturiser. If your hair is still a bit damp, throw your head upside down and dry it with a diffuser.
3. Silky Smooth: Towel dry your hair to remove excess moisture, then comb it through and apply a de-frizzing cream. The next morning, clip your hair up into sections and flat iron one at a time to remove any kinks or ridges. Finish with a shine spray.