HI,
my site got sudden traffic fall from oct 3rd, 2013… and my search impressions also dropped down… is there any algorithm update on 3rd oct??
probably Hummingbird affected you
Google updates its algorithms all the time, sometimes with minor tweaks, sometimes with major changes. We have no way of knowing why your site has fallen. It could just be that your competitors have improved their sites and their positions and have overtaken you, without any changes at Google. Just concentrate on following Google’s guidelines.
If it’s not a secret, what was your main SEO technique? Google might have penalized you for building artificial links or something similar (or as Stevie D said, Google new update favors your competition)… You need to be a little more specific in order to get a more helpful answer.
Hope that things improve for you soon 
There are 120+ possible factors that could effect your website. If you can provide more details, we would be able to help you better than just answering generally.
Most of the time, when your site get penalized, it is pretty much over. Recovering from any penality is a longer process than starting fresh again.
Good luck with your site.
Yes, Hummingbird is new update from Google. First you should check your webmaster account. May be you found error message. Probably your website have another reasons too to dropped traffic.
what is current status of your website?
As the OP has never returned, there seems little point in reviving the thread now.
Thanks to all who contributed. Thread closed.