Is the use of past tense as "let me know if you needed" common?

Yes, it's wrong. It should be present tense need. I suspect the speaker has been misled☟ by the usual clueless nonsense about English having a subjunctive mood.

Students are often told in school that one must "use the subjunctive" in hypothetical clauses. Many interpret this command to mean that, since the verb needed in

• If I needed anything, I would certainly tell you.

is an example of "subjunctive", then past tense must be what one should use with if.

☝(when I was young, I always pronounced this word /'mayzəld/ when I read it; /mɪs'lɛd/ never occurred to me. Too bad -- misle would be a useful word)

It’s not what I’d expect from a native speaker. It seems as if the writer was thinking of something like You wouldn’t hesitate to wake me up if you needed something, would you? but got confused in putting it down.