But, here are the good things about being really tired:
-- I can be a dick to people when I need to be a dick to people. (phone solicitors, door to door solictors, hardware vendors)
-- I hate more things, so I can write them all down and deal with them on a happier day, even if on that happier day I wouldn't normally hate them.
-- I can do mind-numbingly dull tasks which I wouldn't normally do.
-- I don't get side-tracked with thoughts of going out and playing (running, biking, frisbee, etc...)
In conclusion, tired days are useful.