You're not going crazy, and no ... your map is not posessed!

[@laptopnotebook1015]

You can also find very hidden collisions (when you deleted visible objects) by toggle view/show/physics and then press the play button

[@bauerbrown]

You can, but I don't recommend it, especially for beginners. You can inadvertently cause yourself a whole lot of extra work using that method. My ghost in the machine video explains a little bit about what could happen.