Idea: Frame Rate
Imagine a motion picture being displayed on a screen. Imagine that one frame of film is displayed every 30th of a second but held still for only a 60th of a second. Now imagine that another film is displayed at the same rate but in the other 60th of a second. Now image that your eyes/brain can only see one of the two films because your naturally human eye/brain rhythm only fits one of the two films. Both are displayed but you can only see one.
That's the way the world really is (In the story). You see, hear, feel, detect, only one stream of reality.