Hey David,
I was diagnosed with Idiopathic Hypersomnia in May of this year afterhaving tried to live with it for as long as I can remember. High school wasn't too big of a problem for me since my parents were there to tell me to get up if (rather: when) I turned off my alarm and overslept. Once I got to college, though, things got pretty bad. I'm in my third year now and almost failed out. I didn't have anyone to answer to when I overslept, and a lot of people attributed it to laziness so I began to think it was me who had the problem., I was the reason for sleeping so much, the alarm went off but I turned it off and kept on sleeping, and most importantly I should be able to do something about it.

Then I met someone who had narcolepsy and started to realize that maybe I had something too. A few appointments and sleep studies later, made it turn out that I did. Sorry for life story there. I just saw a lot of parallels between his and mine so I guess I'm hoping it'll be at least a small comfort that we've had many of the same experiences. The irritation you talked about is also something I've experienced, but it was much more severe when I was younger (around elementary school). It's still there, but not nearly as bad. I'll try to get you as much information as I can find - I'd rather not try to explain much myself since I'm most definitely not an authority on anything. First, I learned quite a bit from this on:

http://brain.oxfordjournals.org/cgi/reprint/120/8/1423.pdf

It's a study on 42 people with various forms of hypersomnia. Really, its point was to find a line among the different hypersomnias as well as attempt to further distinguish them from narcolepsy, but it does have a lot of very interesting stuff in there about hypersomnia that I hope you'll find useful. Something I was just reading which is worth looking in to as well:

http://www.beatcfsandfms.org/references/IdiopathicHypersomnia.html

From the article, "Delayed sleep phase syndrome is a diagnostic consideration in some patients whose main complaints are extreme difficulty in awakening at the desired time and excessive morning sleepiness. These patients are not sleepy throughout the day, however, and go to bed or fall asleep extremely late at night." I'm not sure how much you feel relates to you but it might be worth looking into. Those are two of the few things I've been able to find that when I really went into the depth, though. Before my tests and after my diagnosis, I searched everywhere for information about the disorder but most of the websites really said the same thing ( http://www.sleepeducation.com/Disorder.aspx?id=48 is a good example).

(Heh - I've exceeded the limit. Gotta break this up into two posts. I should really try to not be so long-winded...)