Number of things this season. Our system is heavily reliant on key players being fit - it only needs one or two from Kompany, Toure, Nasri, Silva and Aguero to be missing for us to struggle to adapt to their absence. Add to that, lack of a pre-season for a few players (those that went far in the world cup), lack of form (Zabaleta and Kolorov provided the most assists of any fullback pairing in Europe last year, both have been pants this season), off field issues (Toure, who regardless of interest elsewhere, clearly didn't have his head sorted for either the world cup or the first few weeks) or loss of confidence (Fernandinho, who has only sporadically showed any semblance of how he played last year since Brazil got tonked) and two players who clearly need time to settle in to the pace of the PL (Mangala and Fernando).
Factor all that in and consider how well Chelsea strengthened in the summer in comparison to us due to the sanctions and the last minute loss of Negredo and the fact that this season, despite not looking good to all the above issues, we are still second (and two games ago, were exactly equal with a Chelsea side some people were saying was the most balanced the PL had seen), progressed in the CL and have equalled a record number of wins in a row without a recognised striker in some of those games, then I would say it is a short term blip.
Or, we can ignore all that and it could be the managers toss, the spanish pair don't know what they are doing and we've got a bunch of players that don't give a shit.....
Personally, I'll stick with short term blip.