A few months back, I have also faced the same issue where my rankings dropped from 48 into somewhere around 170. I found two reasons which might have damaged my rankings.
1) I did not use my keywords correctly:
While performing some off- page activities, by mistake I broke my keywords into parts and did not put the keywords correctly. Doing this confuses the search engines and the ranking might go down.
2) Check out the on-page your website and change it if needed:
I have experienced this, after making on-page changes not only the rankings but the traffic of your website will be improved. Try to perform these techniques and then check your ranks.