To answer the original question.. honestly, I am not sure. I have just always liked the name Anastasia, I think it's pretty and with more than a hint of the exotic (and perhaps I am just a little fascinated by the urban legend of Anastasia Nikolaevna? hah).. also, my given (male) name starts with an A, so I figure it wouldn't be too much of a change to introduce myself as just 'Ana'.. or perhaps 'Asia', 'Tashia', 'Stacy'.. lots of choices depending on mood ^^. I am still not 100% decided on it though, as it's not a common name where I am (no, I am not Eastern European ^^), though I have a cousin named Natasha so I suppose it's not THAT far off lol!
As said though, 'Ana' is a very common name so it wouldn't be hard to pass unremarked.