My Cat is Hissing & Growling TONS!?

I was woken up this morning around 5am by my cat making horrible noises. It looks like she picked up a bag from a recent shopping trip (she likes to lick plastic bags). She apparently dragged it into my bedroom with the stuff in it, she then dumped it out and caused items to fall off my night stand. This apparently scared her into to freaking out. She then hid under my bed and every time i moved she would hiss and growl really loud. She finally quieted down so I left the room. She came out about an hour later, and was meowing that she was scared, so I picked her up, gave her a kitty treat and she was fine. I left for about 5 minutes to take out trash and when I returned she meowed again and promptly ran about 10 feet away, hissing at my other cat (which has lived here over a year with her) and then hiding under the futon growling and hissing whenever I walk past. She just recently ran down the hall and is hiding under my bed. How do I get her to stop this? Usually when she knocks something down she just runs away, why freak out so much this time?