My 9 month old ( 7 months adjusted) will be fast asleep and just start screaming out of nowhere,…

My 9 month old ( 7 months adjusted) will be fast asleep and just start screaming out of nowhere, when I pick her up her legs and arms are stiff and she's basically dead weight and her eyes are glazed over like she's still asleep and she still screams like crazy..once I wake her up and calm her down she's fine and will go back to sleep but it takes several minutes to wake her up and calm her down.. this is the second time it's happened since she was born, any ideas? :( it's terrifying...