Today has been all sorts of busy and weird. I come home in the evening, had bags of groceries with me so set them down, and find that my apartment door is ajar. I experienced some deja vu thanks to this so I stepped back to check the door, it indeed was my apartment.
I was dead sure I closed it behind me while leaving. I was honestly a bit spooked by now, so I left and went back downstairs to check with the security- who was away on a smoke break or whatever. I bumped into my neighbour who said she had been in and out of her apartment in the daytime and didn't notice my door open. So I called the cops, and told them I was afraid of going back into my apartment. They came, checked out my place and it was all ok. Frankly, the only thing of value in my apartment is Kalia, my macbook. Kalia was right there where I had left him. The cops went through all the closets in the house (and there a bunch of them) and by this point my worry had shifted to how messy my apartment was and how these random cops were being privy to it. :)
They left advising me to change my lock and keeping my fire escape grill closed.
The only other explanation I can come up with is that the super came in to check on a leak or something and left it open. But the super really only comes in after I leave him at least 3 nasty notes complaining about something- and he always leaves a note in the door every time he's in the apt. - and none of that was there this time.
I am still slightly disturbed by the whole thing. I hope I wake up to some easy explanation tomorrow.