1. Stare at a problem for two hours over two days, and be confused.
  2. Give up and sleep for 17 minutes.
  3. Spend 6 minutes solving it.

The worst thing about insomnia for me is that it makes my brain generally unable to actually know that it's tired. I might sometimes say that I feel tired, but it's far less often that I actually manage to follow that up with a rest — and so often that's actually all that's required to return things to some form of calm. It's like they say (well, to actual workers, not shinybums like me): if you're wondering if you're thirsty then you're already past the point of needing to drink water.