It was first defined at Legal Insurrection as a "a condition in which one's mood swings up and down in sync with the level of blog traffic." The Other McCain expands on two closely-related syndromes:

• SiteMeter Fever -- A neurosis typified by obsessively refreshing your SiteMeter to see if your traffic has increased since the last time you checked it, seven minutes ago.
• Bloggernoia -- This psychotic disorder involves the suspicion that other bloggers have malevolent motives for not linking you. "Don Surber is just envious of me!"

I have at times suffered from all three. I believe there is a pill you can take to alleviate the symptoms, but side effects include slight cyclopcism, raging halitosis, and clown-foot.