If you are wearing clip-ins, it is recommended that you remove them before going to bed to avoid any unnecessary tangling, and to avoid damaging the clips. If you are wearing hair wefts/weaves or lace closures, it is perfectly fine to wear them to bed. Just make sure to brush your complete head of hair at night and in the morning with a special designed brush for extensions. You should always braid your hair before going to bed, to effectively avoid causing any tangling.