Most often, the reason something is "on your mind" is that...

Most often, the reason something is "on your mind" is that you want it to be different than it currently is, and yet: you haven't clarified exactly what the intended outcomes is; you haven't decided what the very next physical action step is; and/or you haven't put reminders of the outcome and the action required in a system you trust. That's why it's on your mind.