Recently a website has been optimized, has been operating in accordance with conventional methods, there is no black chain link, the site has not been DMCA, but today the view keyword rankings, fell to No. 5 after all, my God, this I hit too much, who encountered such a situation do, please tell me, thanks a lot

It happens all the time, stop checking rankings and it won't bother you again.

Your website will rank differently from person to person anyway..

So for Joe, Your site maybe 50th.
For Jane, Your site may be 1st.

Its normal.