I've quit announcing that I'm tired. I hear the "yeah, I know how you feel. I'm tired, too" response too much.
For me, there is such a huge difference between just being tired and having the dreaded MS fatigue. If I do get the fatigue and someone comments on it or asks about it I tell them I have "MSF" (multiple sclerosis fatigue).
![Embarrassment](images/smilies/redface.gif)
It sounds more severe than just being tired (because it
is) plus it shuts up the folks who want to play the "I'm more tired than you are" game.