Chicken gone mad.

I noticed yesterday that one of our hens has gone mad. I found her walking around the coop by herself while the rest were out free ranging. she would walk into the corner as far as she could, scratch the floor and then jump as high as she could and peck/scratch the wall, then land with a big thud. She did this for HOURS. I tried chasing her out, but she went back in and started the whole thing over again. What gives?