Why can’t I stop thinking of someone I dont know?

This probably sounds crazy😅😂 but I can’t stop thinking about the post man. I don’t even really know him I know his name, age and that’s about it. There has never been any conversation between us other than the usual ‘hello’ ‘thankyou’ ‘have a nice day’ the basic little exchange of words you’d have with a delivery driver. He has been one of the many post men in the area for months now and I never felt like this until a few days ago but I haven’t been able to stop thinking about him. He’s on my mind constantly through out the day and I don’t know why. However I don’t feel anything towards him at all no angry feelings or loving feelings there is no feelinge attached to these thoughts. Just thinking about him, it’s really weird it came out of no where and is getting worse as the days are going on. Has anyone ever experienced anything like this before? Its driving me crazy and I don’t understand it.