I guess I'd think of it something like overhearing a conversation and fantasizing about it. Have you ever had someone wave or beckon to you and you gesture back only to learn they were waving to someone behind you? If the two of them just see each other and not you, then you feel silly only to yourself and you never were part of that sequence even though it feels like you were because you waved to this person, thinking they were waving to you.

I have often had hypnagogic experiences http://skepdic.com/hypnagogic.html when I thought something was happening that wasn't. I've gotten up in the middle of the night and searched my closet for the person that went there to hide :-)

I'm forever dreaming of a phone ringing, so realistically that I wake and listen hard (and have a couple of times jumped up and gone to where the phone is) and I could imagine that happened during a "regular" part of the day. It's common to think one sees or hears something and when one is ill that happens more often? Meds too often heighten experiences; when I got home from the hospital after surgery my pain meds threw my sense of smell way off and I made my husband change the bed a zillion time as the smell of the sheets nauseated me! It wasn't them, it was the meds throwing my brain out of whack a bit. It doesn't necessarily do that to everyone but my genetic background/individual sensitivities being the way they are, that's how it played out.