I have heard both words used recently to mean confused or lost. Which is the correct one to use or is this one of those English/American language situations?
'Disoriented' has been in use in British English since the 1600s, whilst 'disorientated' is recorded nowhere prior to the 1950s. However, both now seem to be treated as options in common usage.
I think the word 'orient/ed' came first, then the word orientation... then the word orientate was formed backwards from that. Of course if you're heading west you're probably occidented anyway.
Anything 'Oriented' has been arranged to face east. So 'Disoriented' would be any turning away from an easterly direction.
Anything 'Orientated' means it has been arranged to face in a chosen direction other than east. 'Disorientated' simply means turned away from the chosen direction.
I've only come across orientated and disorientated in British English. Oriented and disoriented are strange foreign terms to me that I've only come across when reading the writings of American authors. A bit like colours vs colors I suppose. To me it's just a case of which side of the pond you are.
I have personally never, ever read the word "disorientated" in a book. However, I have read the word disoriented in books plenty of times. (most of the modern literature I read is non-fiction, so perhaps the word "disorientated" is being used in modern fiction unbeknownst to me.) I hear people say "disorientated" sometimes, but it just sounds so wrong to me. And for what it's worth, I'm really good with language.