I find this every couple of weeks, it's no bigger than 2 millimeters and I have no idea what it is or where it came from. Those photos are super-zoomed in, snapped from a video recording.

UPDATE: I found this photo online

Commenters of that bottom photo reckon it's a type of flea, but I'm having a hard time finding proof of this nor have I found anyone give any reason as to why it's coming into my house.