Is everything all in your head

I feel like it's a pretty universal sentence (it's very descriptive). In Spanish and Catalan (native for both) it's the same word by word.

In Mandarin the expression would literally be "It's all thought up in your brain." So yeah, same in Mandarin.

what's wrong with "It is everything in your head"? (Not a native German nor English speaker :)

Well truthfully, it's still a valid English sentence but now it means something different. That would mean that everything in your head is "It". Or whatever you are referring to. When you say, "It is all in your head" which is the proper idiom, it means, "All of" It "is in your head." as in, it doesn't exist. That's quite a bit different from everything in your head being it. the all encompassing "all" or "Everything" should refer to "It" and not to what is in your head. does this make sense? Btw, what is your native language?

No, "you're full of it" means "you're lying". On the other hand, "it's all in your head" means "it is all in your head", which is appropriate when something is thought of as reality but is only just imaginary.

:) reminded me of "Nur in mein Kopf" by Andreas Bourani ", one of my favorite German songs.