The same thing just happen to me. My 6 year old site just tanked on July 13th at 3am. I went from 3500 hits per day down to 850. I lost almost all my keywords. I hope it comes back but I had this happen to another site and my traffic still hasn't returned to that site in over a year. I guess I will keep my fingers crossed and maybe make a few changes.
it might be happen that you have changed it's meta tags otherwise google dont rank only you they have many more sites so it happens with all websites.dont worry it will restore its position in 3- 4 weeks with good seo.
Before SERP dropped, I didn't do any changes on the website contents. The only activity going on was having "Blog commentors" to add links, approx 100 links. 100 links is nothing even though they all get indexed. It should trigger any filters. So far, from what I hear: Google seems to be doing something, e.g. update, etc. Some people get their keyword SERP back after a short period of time. Some people don't get it back even after a year. I'd not say never as you never know. I'd like to hear from some guru from their experience what I can do now other than waiting.
adding to my previous post, when my serp dropped.... it has nothing to do with competition because I have another website in the same niche that is pretty small and has ranked higher than it which is impossible!
I just checked the SERP for my site again. I'm so happy to see the ranking for my targeted keywords are back with some minor improvement. But the PR remains the same.
My traffic just returned yesterday to my site that took a 70% hit from google last year on June 27th. My site that tanked four days ago still hasn't returned but I ain't complainting. At least I got one site back, for now!