Separation anxiety?

Hey ladies, really hoping someone can help me out. So my daughter finally started sleeping through the night but all of a sudden started waking up around midnight completely hysterical. When I go in to comfort her and rub her back she quiets down immediately but as soon as I leave she throws a fit. I’m thinking separation anxiety has started. Is anyone else going through this?? What helps? Should I keep going in to comfort her or is it better to let her cry? It seems like going in makes it worse.