to have a lot on one’s mind (to be worried about many things)
A: Why are you so quiet? Normally, you can’t stop talking.
B: I’m sorry. I’ve got a lot on my mind at the moment.
A: What like?
B: Money worries, job worries, family troubles…lots of things!
A: Have you seen Simon lately?
B: Yes, I saw his yesterday. He seemed to have a lot on his mind. I’m worried about him.