Sent shivers down my spine reading that - I cannot begin to imagine what that feels like - so creepy - was it someone you knew or some random weirdo?

I can't say that I have. I've met weird ones that tried getting too close, too soon. But, no real stalking. That I know of........

upperclassman in med school

The experience was traumatic enough that it still has you shaken. You should look into counseling services in your area. Trauma of any sort is the type of thing that you should never take lightly. It will eat you up inside and is more harmful than the thing the traumatic experience. You don’t have to live like that and you shouldn’t. Find the nearest trauma counseling services to you and talk it out with someone who can help you cope with the anger and the fear.

My ex wife stalked me for years after we split up, sometimes just checking on my family and other times hacking my social media

Not that I know of, but if they're good idea never know. Have you ever had a bad stalker?

NNNNNNNNo.

I didn’t have a stalker but I had a classmate who made me extremely uncomfortable. He didn’t have to stalk me because we saw each other every day any way. At first I liked him but then I realized he was really not a good match we were too different. He started turning my classmates against me and even though he didn’t show up anywhere he wasn’t supposed to be I had to see him all the time and he just wouldn’t stop being mean rude and talking about me behind my back.
He never did it but I was always afraid he would show up.