Romper discusses the difference between sleep regression and separation anxiety, which can look the same in young children.

So, how is separation anxiety different from a sleep regression? According to the Sleep Lady, Kim West, a Licensed Clinical Social Worker (LCSW-C), separation anxiety is part of an important developmental milestone, called object permanence, or recognizing different faces and places. Your baby “suddenly understands that when you leave the room, you don’t disappear like a game of peek-a-boo. Suddenly, [your child] is hit with the realization that you can go somewhere without [them].” The thought of you leaving can be pretty overwhelming and, as a result, can cause anxiety.