Dechaine,
Good question. I know in theory it is possible to get too much sleep, but I really think we vary a lot with how much we need (like with everything else.)
In your case, you're genuinely tired, and you've been working - it's not like you just hibernate in bed all day to escape. So, if that's what your body is asking for, I'd say it probably needs it. That is, unless you've noticed that you feel better with less...
I have a good friend who's the picture of health, and she sleeps 10 hours a night, year in and year out. Then she goes like a force of nature all day long.
I have to force myself to start getting ready for bed, way too late. Chronically tired....lifelong habit. If I could afford therapy, that would be one of the first things I'd try to figure out. The definition of insanity, and all that ;)
Debbie