I have a great life – a job I love, a girlfriend I love, a tasteful apartment I love – but there’s one catch. Jeff is stealing it. Jeff is this random dude who just moved into my apartment and started taking over my life. I don’t know who he is or how he does it, but he just gracefully assumes my every role. Weirdly, although he looks nothing like me, everybody now thinks that he is the real me and I’m just a stranger. I went to work and found him in my cubicle scoring facetime with my boss who, by the way, asked me who I was and what I wanted before having me escorted from the building. This morning I walked in on Jeff whispering and giggling with my girlfriend. She called him by her petname for me and asked why he hadn’t told her that he was having guests. Jeff said: “Honestly, hon, I have no idea who this guy is. He just showed up and started living here. I haven’t had the chance to change the locks yet.” Alistair, what’s happening?
Usurped in Kanata
It sounds like you may have slid into an alternate universe while you weren’t looking. Contrary to popular belief, that doesn’t necessarily boot out your alternate self, it merely moves you to the corresponding part of the new universe.
Throw your mind back to the events immediately preceding the appearance of Jeff. If there were any visits to particle accelerators, nuclear plants, or sleep study labs, things should have an obvious path of procedure. If not, simply recreate a period of two weeks in as close detail as possible.
When you do slide to another universe, assess the situation. Does the local version of Usurped resemble you? If not, move on. If yes, remain. He is either there (in which case, see my comments on Dopplegangers), or he conveniently vanished a short while ago (in which case he is cycling through an enormous number of possible existences and won’t bother you anymore).
On the other hand, you may simply be losing your mind or being erased from public consciousness. In that case, assault Jeff for free housing and medical care.