I know when I'm tired when I play TF2 for four hours but continually lose.
Last night I also made an epic chasm in infdev. It was a good 24 blocks down in a 9x9 space. That's basically 81x24 stone blocks I mined. Theeeeeeeeeen infdev crashed. That was the biggest FFFFFFFUUUUUUUUUUUUUU ever
I think i don't suffer from insomnia, but my sleep schedule is heavily broken.
When i don't have to work, i am awake for 18 hours and then sleep for 12 hours.
Sad thing i have to work at more or less fix times, so i go to bed at 3am and only have between 3 and 4 hours of sleep.
This usually results in getting ill after a month or two.