Arsenal were on top of the league for a few weeks but now find themselves at 4th, after losing to Fulham, away. It's still a very tight title race though with both Liverpool(a game in hand) and Aston Villa at 42 points and Arsenal, Man City at 40. Spurs are at 39 points, right behind them. Most teams are having an injury crisis and with players going in for international duty, there's going to be a lot of drama and change, in the coming weeks.
A decline in performance after being at the top of the standings happens very often to Arsenal, last season Arsenal managed to dominate the standings for a very long time, in the end they had to be satisfied with seeing Manchester City come out as champions. This season Arsenal bad habits have not been overcome, two defeats and one draw in the last three matches means Arsenal have to settle for being in fourth place.
Currently, Arsenal is not far behind Liverpool, who is at the top of the standings, but losing points to Fulham and West Ham makes Arsenal's position even more depressed. It is very possible that there will be a change in position in first to fifth place because the point difference is very close. This season the surprise came from Aston Villa, they managed to rank second after appearing impressive since the start of the competition.