My 5 month old screams in her sleep?

I have a three month old and she did the same thing. She will slowly fall asleep and then she would wake up suddenly and start screaming. I think it is because she startles herself when she wakes up. And she isn't aware of where she is because she feel asleep in my arms and then wakes up in a dark quite room. But once she finally falls asleep for the night she is fine.