I would be terrified. I don't know what your school is able to do, but do what you can to keep your home location private. Like everyone says, document EVERYTHING. He may well be ill, but that doesn't mean that he won't act out inappropriately. Weapons at school? No. MacGyver? Yes.
This is what just kills me about taking our shoes off at the airport and TSA and all of the other stuff we do now. Prior to 9/11/01, if someone hijacked an airplane, they took it somewhere. It didn't always work out well, and it was horrifying, but you know and I know that except for the plane that missed the Pentagon, EVERYONE thought that they were going to land somewhere. And what did they have? A couple of hours of flying school and box knives. No one can convince me that if people knew what the plan was that they wouldn't have used whatever was in their purse or pocket to take those guys out.
Get yourself a trial sized can of aerosol hairspray or deoderant and keep it in your pocket. Never go to or from your car whether you are alone or with someone without your hand on your hairspray in your pocket. You've documented this now and you've told him to leave you alone. You're afraid and disturbed and you have every right to be. If he approaches you again, spray him in the eyes with your hairspray. Is it a weapon? No. No more than my fingernails are a weapon. If someone invades my space when I told them to leave me alone and I scratch their eyes out that's their problem I happen to have vicious fingernails. It's his problem you happen to have a can of trial size spray in your pocket. Just don't tell anyone your plans, that may turn it into an assault on your part. You have to be able to convincingly argue that you were surprised and that hurting him "just happened".