Why does my 13 month old wake up screaming?

My 13 month old baby has always fell asleep in her crib between 7-8 and never wakes back up after asleep or wakes up till 9am. but for the past 4 nights she wont go to sleep by herself and if i put her to sleep then lay her down in her crib she wakes up and screams and crys tears and says mama! she has never done that before. like i said before she use to sleep fine by herself then all of a sudden its like she is scared to be in her crib in her room alone we have night lights. any ideas y or what could help?