preoccupied with; obsessed with; only thinking of
Idiomatic expression meaning one's mind is completely filled with a particular thought or worry. Often used with ～で or ～のこと.
My mind is completely occupied with tomorrow's exam.
She was obsessed with ideas for the new project.
気になる is a broader expression for something being on one's mind, not necessarily to the exclusion of everything else.
Standard kanji-kana mixed spelling.
Kanji spelling for いっぱい; less common but still seen.
Literal meaning 'head is full'; idiomatic extension to mental preoccupation.