That was probably Ozil's poorest game in an Arsenal shirt yet (still good, mind). I think his tweet explains why
He's still not used to the pace of the premier league, he looked exhausted at the end.
Does the same happen when he's playing for Germany?
Might just be Mourinho.
No, it usually doesn't happen when he plays for Germany, at least not like in Madrid. And from what I've seen, it doesn't happen so much for Arsenal either. At least he scored a late goal against Norwich and was quite active in the last part against Liverpool, and other games as well. He was a bit jaded in the Crystal Palace game, after basically playing all games for Arsenal and Germany without much rest.
About his performance: I don't hink he was that poor - but it depends on what standards you go by. Compared to his standards and to what he is capable of, it wasn't a good game, that is true. But his vision and movement off the ball was superb. He switched positions with Cazorla and Rosicky quite nicely, pulling Liverpool defenders to the sides and thus opening up space for those two and Ramsey. The assist for Ramsey was great too, fooling 3-4 Liverpool defenders with one pass.
In general, as I said before, I think he's been sacrificing his game so far because of a lack of width in the Arsenal game. Without some fast wingers that can pick up his passes, like Walcott or Podolski, the middle becomes a little congested so he usually has to drift to the sides a bit, which opens up space for Ramsey to shine but of course isn't good for his own game. So far, he has been wasted a bit. Once the wingers get back, we should start to see the best of Özil, and I can't wait.
Then there's the issue of not having fully adapted yet. He had an amazing start at Arsenal, but I guess he still needs bulking up a bit, getting used to the pace and physicality of the EPL more and grow chemistry with Cazorla and the other players. Give him a bit of time and things will flow. Still impressive how fast he performed so well in many games, that was not to be expected.
Also, what is great is that he can have a quiet game but still provide an assist/show other glimpses of brilliance.