What just happend with my dog?

Ok so i have been outside with my dog practically all day. And i just went outside to see her she went mental. She randomly started growling and barking and showing her teeth, im pretty sure she new it was me because i was telling her to calm now and saying her name in a calm voice and stuff. So she calmed down and i started petting her, i walked away to untangle her chain and out of no where she ran after me and bit my knee. She didn't cut my but her teeth are very big and it hurt my bone in my knee. IM actually scared to go out there and see her now.And shes only 11 months old (german shephard) ... So what do i do?