Please help! Something is wrong with my Cat?

My year and a half old cat Rosie has been acting very strange all day. Usually she's very quiet and loves many cuddles and attention. She always snuggles up to me and licks my cheek when I hold her. Today, she's been hissing at me and my parents and she's growling at us. She's slept most of the day and barely touched her dinner. Something isn't quiet right with her and I don't know what it could possibly be? Please help me out here, I want Rosie back.