Why does the inspiration come at night, when all I want to do is sleep?

Last night, for over an hour after I'd intended to be asleep, I had visions of events 175 years ago dancing in my head. Finally, a reasonable, rational, logistically feasible course of events that ended up with three people dead, in such a manner that nobody's character was compromised, and set in motion events that lead to four romances. That's cool! I'd always hated my previous take on events, but hadn't been able to fix it. And I wrote it all down so I wouldn't forget it...

But why then? When all I wanted to do was sleep? Why not this morning, when I'm sitting in front of my computer waiting for inspiration? And now, after being awake so late last night... all I want to do is sleep!

Obviously that is one of the unwritten rules of writing:

Inspiration will strike at the absolute worst moment, and when you sit down to do something with said bit of inspiration, nothing will be there.

Sometimes I wonder why I am so set on being a writer...