Was he injured after Chelsea, he was a beast in that game and then seemed to be poor for a while after that? Can't really remember. Last season he was unbelievable until the QPR game, M'bia bullied him all game and after that his performances dropped off a bit.
I think it can also be down to him having to play with Parker after that game. Parker was as diciplined as a puppy, and left his position all the time, either to run with the ball until tackled or to chase an opponent all over the pitch. Poor Mousa had to stay disiplined in order for us to not be overrun in midfield.
He had to restrict his attacking play more in the second half of the season. One of his best games was at Anfield, where we played with Livermore-Parker in the centre, and Dembele could drift around knowing that if we gave away possession, it wasn't necessarily up to him to be in a holding position.