Best suggestion is to visit Web Masters tool and check if there is any message from Google. If it says Google sees your website as suspicious and black marked, then this could be serious if not, the most likely causes are Google Update effect, or your website might be possibly hacked (this is more so if you are using wordpress).
Either way there is no need to panic, If your website has too many Paid links then you can remove them and ask for reconsideration to Google (Via Google Web Masters tool), if it is hacked, it is even simpler, ask your developer to patch it, or upload an older version (from backup) and your website will slowly recover. All the best...!