too close/trying to catch me alone/following me around/whatever."
So if someone comes to you with a problem you are not seeing, think about how you differ. They could be seeing things that are not there, but they could also be seeing things that are not there for you, but there for them. You may not be able (or willing) to do anything without evidence, but you can keep an eye out for developing problems, or put measures in place to prevent things from escalating. First and most of all, you can at least listen.