Your positioning on the search engines such as Google can have a huge impact on the amount of traffic you get to your website. This in turn has an effect on the number of sales and enquiries that your business receives.
If you track your search rankings then you may notice a drop from time to time. If the drops are only minuscule and other search terms have gone up then it is probably just the normal fluctuation in results but if all of your search terms or a large number of them drop substantially overnight then there is probably a serious problem.
This often happens when a website has been penalised and demoted or removed entirely from the search engine results pages. Websites often get penalised or demoted due to issues with pages not loading, slow speeds, duplicate content or if you have recently undertaken some black hat techniques.
It can be very hard to recover from substantial drops, but you need to first establish exactly why. Once you know this you need to ensure that the problem is fixed before resubmitting to Google etc. for listing. There is no telling how long this will take, so in the mean time you may wish to try other avenues of marketing such as social media or Adwords to build up your traffic.