it happend to me as well
in 1980 i fell from a low wall which i slipped off (whilst running away from some of the skool bullies) and landed on my head. Ii suffered a blackout, severe concussion, brain damage, (oh and it hurt like hell!).
Thanks to this little stunt i spent a week in hospital after a number of head xrays with suspected fractured skull. (I also ended up OD'ing on paracetamol and aspirin because of the severe headaches for the following year or so, and now have a liver that looks like edam cheese.)
I then spent the following 6 months or more walking around with an American accent.
This was really-really not funny, and my life at skool was made hell by all the (then 80's chavs).
For the following couple of years i would on occasion drop into an american accent when under stress, eventually my accent changed to full on BBC news presenter English.
(yeah too much TV really is bad for you, especially all those late night politics programs).
Which got me into even more trouble with the oiks who all spoke with a broad devon accent.
we also had all those alien spaceships being observed over devon in those years..... what a pity i wasnt abducted as well...
i could be flying about in a spaceship or be used as an experiment, instead of on the long term dole, wasting my life away typing this rubbish about my failed les-miserable life on a late tuesday afternoon...
btw... Need more frequent BOFH episodes :)