YOU SAID:
I've got to use my head and think!
INTO JAPANESE
私は頭を使うと思う持っている!
BACK INTO ENGLISH
I use my head and have!
INTO JAPANESE
私の頭をしている!
BACK INTO ENGLISH
You are in my head!
INTO JAPANESE
あなたは私の頭の中は!
BACK INTO ENGLISH
You are in my head!
That didn't even make that much sense in English.