Continuity mistake: When Yoko first talks to Emma, to the right of Emma is a striped blue shirt hanging over a lampshade. Between two shots, the position of the shirt hanging on the shade differs. (00:04:35)
Continuity mistake: When Yoko opens the door and ventures into the attic, the slide-door she pushes is nearly fully open. Yet when we see the shot of Yoko's legs dangling, the door is now much further shut. (00:06:20 - 00:07:35)
Continuity mistake: When Karen and her boyfriend talk on her bed, and kiss, between shots Karen goes from having her head unsupported, to her head resting on her hand. (00:09:10)
Continuity mistake: When Karen and Doug are walking down the street, right before talking about the Buddhist ritual, they are holding hands (right before turning a corner). In the next shot (right after turning the corner) they are not holding hands at all, and these two shots are supposed to be connected. (00:10:20)
Continuity mistake: When Karen first goes to Emma's home, she opens the door, then the camera pans over wrappers and rubbish over the floor. Then it cuts to an overhead shot, and all the wrappers and rubbish have moved around and differed position majorly. (00:14:35)
Continuity mistake: When Karen goes into the cupboard upstairs, prior to meeting Toshio, she picks up a book. In one shot she picks it up by the page side, then when it cuts she is holding the spine side. (00:17:40)
Continuity mistake: When Matthew arrives home at Emma's to find the place a dreadful mess, just before he walks over to Emma, who lays in her bed, the pieces of paper/rubbish that are around/near the pot of noodles, change and differ between shots. (00:31:55)
Continuity mistake: The message Susan leaves on the answering machine is a little bit different when Karen first hears it than when the detectives hear it again later in the movie, and when we actually see Susan leaving it.
Continuity mistake: When Susan leaves her apartment when Matthew rings the bell, the door slams shut behind her. When she turns around to go back in, the door is open.
Continuity mistake: When Karen is on the ground towards the end, the gas container lid is on, but in the next shot the lid is off.
Answer: I don't think she actually went back into the past, I think it was just the house showing her what happened, or at least a type of visual echo of what happened. After all, some pretty strange stuff was happening in that house.
Mad Ade