This may be due to the sheep are being held in a strained space, causing a collective frustration. Sheep as well as many other animals and insects have a flock mentality. They mirror each others behavior, which is an instinct for survival.
I have heard some friends talking about the circle phenomenon comes from the poles on Earth are about to shift. Though, I find this unlikely as I have seen this phenomenon many times years ago with insects and other animals. It is not exactly a new phenomenon.