Can definitely relate to that. I'd rather think that there's something temporarily wrong with my brain chemistry, something that'll get sorted out after a few years pass and new habits and a new rhythm, a new balance of social, work, rest, exercise etc become part of my life.
On the other hand I'm afraid that it's a generational thing. A child of the financial recession (nearing 25yo, economy's not quite booming in Europe), of digital work (I'm able to pay the bills programming from home in my own little company without having to leave the house much), of an age with unprecedented access to information (everything you mentioned, knowing exactly how great the world is and how insignificant anything you do is). As if my particular blend of person in this particular age in this particular economy is just begging to become a shut-in.
I didn't quite ride a wave of easy employment that led to company life playing a big social, professional and personal (confidence etc) role in my life, having graduated during a recession. Wasn't forced outside and into the lives of others due to the digital age allowing me to make a living from home.
Anyway it's all a bit depressing, I try not to spend too much time explaining why. It feels like giving up, or finding an excuse.
One thing a friend told me a while ago stuck with me though... on how the notion that life is malleable (this sort of variation on the American dream. That if you just work and try hard enough, you can become anything and do anything), meant as an uplifting and motivating cultural idea, not to mention an idea that homogenizes everyone: everyone is capable, everyone is unique and special and important and powerful... I think perhaps is the reason of so much depression and anxiety and uncertainty in young people today. Because it's simply not true that anyone can become the next Steve Jobs, yet because of this notion that life is completely malleable, if you're not awesome then there must be some unique character flaw you're suffering from, it's your fault.
Anyway again I don't like to get caught up on this frame of mind too much as it just gets me absolutely nowhere, but it's definitely interesting to discuss every now and then.