Somebody Please Help! What's wrong with my cat?

My Cat is 13 and just now she was sitting on my bed while i was doing homework, i felt my blankets shaking a bit and i turned around and my cat was shaking violently breathing hard and her heart was racing, her eyes were shaking and everything and then she finally started to go back to normal that happened once before right after she threw up a hairball but not this bad, and now shes shaking her head and ears and scratching one side of her head so much the fur is being ripped out, shes drooling a bit too, please someone help i'm so scared, what happened to her? and what should i do next?