As others said there was an algorithm change. Google rolled it out first in the US in February. They just made the changes worldwide last week, so you're probably seeing backlash from it.
How to get it back:
1. Write more articles.
2. Diversify your online writing. If you only write here then check out some other sites, too.
3. Analyze your Google Analytics data to find out what IS bringing traffic and what dropped.
4. Make sure content is 100% unique and in one spot only.
A lot of people were impacted. HP lost a lot of traffic, $$, etc.