As a native (British) English speaker, I have to say I think this is highly idiomatic and, possibly, dialectal. Whilst, upon reading your question, I assumed being "off one's pickle" was a euphemism for being drunk, I was not certain about this and it is not a phrase I am familiar with. I'm not sure I would advise adding this phrase to your English repertoire.
That being said, adding colourful phrases to your speech is a great thing to do and native speakers can often infer the meaning even if they have never heard the phrase before. If you like the phrase being "off one's pickle" then feel free to use it.