Wow - a post! I was about to give up on this site...
Yeah, sleepiness is tough - especially in a situation where you shouldn't be sleeping. And I guess that's the kicker. When you're in bed, you can just let yourself go to sleep.
Fatigue may well be toughest, as it seems like unpleasant states are easily encountered: frustration, anger, sadness...
By far the hardest times in my day are around 2:30-3. I'm sick of being at work, and it's difficult to be open to that feeling. I guess because I notice how my body reacts and it's effects, but those effects linger - they don't seems to move on. Sometimes there's only so much you can sit there and notice
On the other hand, when I sit half lotus, there is slight discomfort in my muscles and it seems I can sit there and be aware of that for hours.