Why suddenly my site visitor goes down?

[Rabin]

I think a lot of the answers here make a lot of sense, and you should consider doing them if the following does not work, but I am nonetheless apprehensive about them because of the dramatic drop to nearly zero. This indicates that your usual visitors (that would normally visit your website without google searching for it) are not getting registered.

The first step I would take is check whether your tracking code etc. is corrupted, removed, or hacked. Then, remove filters and log on to the site yourself and see whether it registers.

It is quite unusual, even if you're penalized by Google, for it to go down to zero from 1000.