I have just realized that when I really get In the Zone ... I can quite literally blot out the world around me.
I've been wearing headphones, listening to music at a reasonably loud volume, while I've been doing some on-screen reading here at the computer. I just skimmed back through my Winamp playlist. Songs #61, #70, and (I'm currently on) #77 all trigger specific memories of having heard and registered the song playing in the background -- the lyrics briefly caught my attention. Most of the ones in between ... nothing.
I haven't gotten up from the computer, taken my headphones off, or fast-forwarded through songs -- and yet I stare at those song titles and think, "Oh! That's a good song I haven't heard in a while. I should queue it up."
Some pretty distinctive stuff, too. Like the Waybacks' "Compadres in the Old Sierra Madre," which happens to be right within my vocal range and a great song besides, so I almost always (when able to not make a fool of myself) start singing along or at least tapping my foot. And the Rabbit Joint's "Legend of Zelda" remix -- how the heck does one ignore that? It's second only to "Music of my Groin" in the canon of "brain ... melty ... now" lyrical game remixes.
I assume that this sort of focus is a fairly common experience (or at least have been around enough hackers to not really be surprised by it). What really surprised me was the totality of it. I would have expected some sort of dim delayed realization that the events had occurred ... but no. A complete gap.