I have your answer, it's paranoia, when playing games alone with no background noise or people with you your brain is like: "But what if... You're not alone!" and start to make you see things out the corner of your eye and starts making even the most subtle of sounds a bit creepy. You know that giant dark room on Construct? That's a big contributor to paranoia, it's the lack of visibility that makes you feel like your not alone, try playing on the day map with a YouTube video or something in the background and see if you still feel weird.

Its The Beauty Of Source My Friend, alot of source maps can make you feel...alone, espically bigger maps such as this, however, if its populated enough, you may not feel AS creeped out, personnally, i don't get the creeps while playing source maps, but thats prob because i've become so adjusted to being alone and being on sourcemaps in general.

play with the stalking spy npc, then, you won't be alone.