Our blog post disappeared from the SERPS?

We had a blog post that ranked on the second page of google for a specific keyword, we were getting a lot of traffic and clicks through it. Magically, I noticed we were no longer receiving traffic to that post. When I search for it in google its no longer listed on the second page. I went through 10 pages and still haven't found it. The only way I can see it is if I type the keyword + brand name. What the heck actually happened?