Implies a personal concern or something causing worry, not just casual thoughts. He's been acting strange, and I can tell there's something heavy on his mind.
Pro Tip 2/3
Seeking Comfort
Used when someone wants to share concerns or seek advice about their worries. You seem anxious, want to talk about what's on your mind?
Pro Tip 3/3
Not Literal
It doesn't mean someone is physically placing something on your head. The phrase 'get off your mind' means to stop worrying about something.