A night light can help prevent this behavior.

This is a common occurrence among cockatiels; however, any sudden movement or noise may throw any bird into a panic in the darkness of night, causing it to fall from its perch, thrash against the side of the cage or injure itself on toys or dishes in the cage. If your bird has experienced night thrashing, keep it calm, and treat it for any injuries. The best defense against night thrashing is a night light installed in the bird room or aviary.