The Paradox of the Eternal Now

I was struck by a poignant thought last night while crossing the no man's land between wakefulness and sleeping. I was hovering on that silken line beyond awake, before sleep, where all existence is concentrated in the immediate now, when this thought hit me. All we ever live in is the timeless now moment. How can there exist a past if we perpetually dwell in a timeless state? The very definition of past is predicated on time passing, but there is no time in the timeless present; therefore, there can be no past. The same logic holds for any potential future; if there is no time to pull us forward from the present now we are always in.