oh it's happened to me as well.

for me... usually lasts about 1 or 2 week- and usually about totally random things that i've not even had any interest in before

what usually happens with me, is someone would mention something... and despite the fact i've never heard of it, the next week or so would be devoted to it

my last 1 was about how people lived during the victorian times... don't ask me how that started because i've got no idea

what about you- are they topics you are interested in?

or like me.. just random things