You need to diagnose what make it happen, it's important to determine the kind of drop your site has suffered, is it a single keyword drop, entire site, Google's search algorithm updated, If you’re practicing good SEO it’s unlikely you’ll ever face a Google penalty. However, if you make a mistake, and either intentionally or unintentionally implement some Blackhat SEO tactics, and see your SERP rankings take a hit once Google wizens up, you can always fix the issues that caused the penalty and recover your site’s Google search performance.
Every site is different, and there's no single solution that will work for every problem every time. If you in doubt, consult an expert in SEO for assistance.