It should be bad, at least it will be bad for your health. I am a junior high school girl. Anyway, every night when I don't do well in the exam, my mother will let me sleep in my tunic. Also let me wear a silk bra and core-spun silk pantyhose (if it is winter, I can wear velvet pantyhose to keep warm), so my mother can allow me to wear them all before going to bed. It was very uncomfortable to wake up the next day, especially the tight waist underwear, which made my lower body ache. Therefore, it is not recommended to sleep in corset underwear for a long time.