I have also heard of people who drink human blood and gain nourishment from it. CSI even did and episode on it.

The thing is, drinking blood will make most people nauseous. It's not because it's harmful in any way (aside from diseases, but we're assuming a clean blood supply), but it's the taste and consistency that does it. Soured milk won't hurt you at all either (again, as long as it went sour in the refridgerator and doesn't have diseases) but the taste, texture and smell causes most people to vomit.

Obviously, consuming your own blood is of no benefit since you had to make it in the first place.

You can't say blood isn't a good source of nutrients, because it is! It's just normally not enough to sustain a human. Some tribes in africa actually make milkshakes with milk and cow blood and drink them, so blood consumption is nothing new.

The medical world is still debating the issue of people who need to consume blood to survive. I doubt there will be any serious consensus on it any time soon.

I've heard there is a disease out there that people have, where drinking human blood is a necessity for them to survive. Not vampires, but something else. Is there actually a disease like this?

BrightEyes09, this is an old post but since you asked... Some people say celiac disease causes a craving to drink blood. There is a psychological disorder called Reinfeld Syndrome, named after bug- eating Reinfeld in Bram Stoker's Dracula. RF occurs in people who feel a pyschological, not physical need to drink blood.
On a side note, 2 diseases that are mistaken for vampirism are porphyria and Xeroderma pigmentosum. These disorders involve skin sensitivity to sunlight.