It would help if it was paranoia. All the windows closed would ease your mind from thinking someone was watching through the window. One question for you, does the thing watching you seem to be of fowl intent?
I've had moment in school where it feels like I'm being watched and then like something is so close it's breathing down my neck. And in resteraunts o always sir in a corner seat faceinf outwords so when i get that feeling i look in the general derection it goes away and i can eat in peace. (lil insanity..... Possibly) It isn't fun but it could be extreme paranoia.