I guess we're all stuck wondering what type of immortality you have, but it's not like it would be tattooed on your chest or in a user manual or something. Depending on the type of immortality, it could take you a long time before you noticed. If you still aged, could still get sick and injured and still needed daily sustenance, you'd probably be a couple hundred in before you realized you were in for the long haul.
"I've been immortal on this planet for two hundred years and haven't done anything with my life! Oh. Well, oh well. Whatever, I got time to do something with this super power later. Time to get online and give a first hand account of some historical conspiracy I could potentially have witnessed. Again."