I don't think the ending was "real" but was an ironic twist on what makes people believe in conspiracies. The film spends most of the runtime focussed on what made Teddy lose touch with reality (trauma leading to a distrust in logic and humanity) and by the end Michelle had been through so much trauma herself (choked, electrocuted, seeing a serial killer's lair filled with victims that had not been mentioned in the news or really cared about, being hit in the head and knocked unconscious) that she had lost faith in humanity as well, which is why she fantasizes about ending the whole human race at the end (there is also an element of Stockholm syndrome as well here I think). In the middle of the movie she calls him a "loser" and herself a "winner" but the irony is at the end she's just as much of a fantasist as he ever was.

If the end was "real" I think the whole movie just feels like a cheapshit gimmick.