Same here, no idea what will come out of my mouth either, and it's in my head as well. For instance, thinking I've been here four and half years, I hear in my head "four and a hahf years", and I just think, OMG. :-/
I think if one wants to keep their American accent as much as possible, you better concentrate on thinking and saying things that way, else it's going to sneak up on you as it has me. I was sure that I wouldn't lose mine, but I do make a small effort with my young children to repeat words in their accent so they won't be singled out in school, etc., and I think that's what's gotten me after just 4 and hahf years.
![Wink ;)](https://www.talk.uk-yankee.com/Smileys/classic/wink.gif)
I have picked up the slang and a whole new way of speaking as well. For instance, I never used to say "as well", now I do all of the time.
What a hodge podge of voices I feel like. (See there, it used to be that I would have put the end of that sentence on the front.)
I find it a little unsettling at times, but it's interesting, and probably will be confusing to my family the next time I'm able to fly home for a visit.