It’s okay to sleep with some types of hair extensions attached to the head.

Any type of sew-in hair extensions where the hair is sewn into tiny braids, is definitely safe to sleep in.
The same is true for fusion (hot, cold) or similar glued extensions. Also it is fine for taped extensions or those attached with beads, snaps or clips.
It may or may not be okay to sleep with temporary clip-in hair extensions. Temporary hair extensions are designed to be taken out before sleeping to prevent knotting, tangling and the clips applying undue pressure to the hair roots and scalps.
If clip-in hair extensions are slept in by accident or just every once in awhile it probably will not hurt, but it should not be done on a continual or regular basis.
Your clip-in hair extensions should always be removed before sleeping, exercising or taking showers if you want them to last as long as possible and your want to protect your hair roots, scalp and hair.
If you want hair extensions you can sleep in, get the more permanent sew-in, fusion, glue, taped or permanent bead types.

Any type of sew-in hair extensions where the hair is sewn into tiny braids, is definitely safe to sleep in.
The same is true for fusion (hot, cold) or similar glued extensions. Also it is fine for taped extensions or those attached with beads, snaps or clips.
It may or may not be okay to sleep with temporary clip-in hair extensions. Temporary hair extensions are designed to be taken out before sleeping to prevent knotting, tangling and the clips applying undue pressure to the hair roots and scalps.
If clip-in hair extensions are slept in by accident or just every once in awhile it probably will not hurt, but it should not be done on a continual or regular basis.
Your clip-in hair extensions should always be removed before sleeping, exercising or taking showers if you want them to last as long as possible and your want to protect your hair roots, scalp and hair.
If you want hair extensions you can sleep in, get the more permanent sew-in, fusion, glue, taped or permanent bead types.