Around 8 months was the start of a whole sleep regression phase here - the transition from three to two naps a day plus DS was learning so much more - 'wonder month' more than a wonder week here! (and it wasn't all that wonderful, I can tell you!). Could it also be teething (I know, I know, everyone says that!)? I also agree that the change in routine and environment could be putting things out of whack. The flying could have hurt her little ears (I am a terrible flyer and my ears are sore/blocked for 1-4 days after flying) so it might be worth getting them checked if things don't improve.

Lots of people who go on holidays with little ones say they're atrocious for a couple of weeks after they get back.... not that that helps!