You don't have to keep your hair down while you sleep. You can always put it up for the night. Here are a few hairstyles that it's safe to sleep in overnight and into the morning:
1. Sleeping with Braids
This tutorial has a few ideas for wearing your hair while you sleep. If you have short hair, then you can try wearing a beanie to keep your hair in place while you sleep. However, if you have long hair, then you can try sectioning your hair into three and braiding it. If you want loose waves, braid it loosely. If you want tight waves, then braid it tightly. When you take your hair out in the morning, you'll have a hairstyle ready to go.