When I'm trying to get the early school years child, the nursery toddler and the one-year-old out the door by 8.45AM, I often forget who I am altogether. I just become this screeching sheepdog, trying to herd cats into galvanised buckets.
Seriously, I don't have time to ponder the finer points of nationality most days.
I still have an American accent. As long as I get my point across I don't really pay attention to how it sounds.
I haven't set foot in the US in 8 years, we had a large-ish family in a relatively short time, moved twice in a short period of time and have limited funds, so I haven't really had the chance to get back. My folks are here now, and the US seems even more foreign to me in some ways.
It's a matter of the space/time continuum and just living your day-to-day life, IMO, not 'forgetting'.
Being American is just a part of who I am, and now I've got many responsibilities and am many things, it's not something I get the chance to ponder often.