Can't sleep. Long run coming.

The way my current running/workout schedule works is this:

3-4 mile run 3 times during the week
1 yoga and/or aerobics workout during the week
1 long run on the weekend

It's been a great regimen for me, especially when I was training for my half marathon this past March.  However, I've run into a huge problem lately that I just can't shake - when I know I have a long run in the morning that I have to get up for, I can't sleep.  Literally, I cannot shut down and drift off. 

Last night, I went to bed around 10pm, knowing that my alarm was going to go off at 4:50am so I could get my butt out the door for a 8-mile run.  I had actually contemplated doing 6 1.5-mile laps of my neighborhood last night so that I could sleep in this morning.  I didn't, because I was lazy and because the husband was worried for my safety, and thought I'd just do it in the morning.  10pm, no sleep.  11pm, no sleep.  12am, no sleep.  1am, this is starting to get ridiculous, why can't I sleep.  I'm exhausted, all I want is a few hours before my run, and it's just not happening.  I think I finally drifted off around 2am only to be awoken by my bladder at 4am.  At that point, I just gave up on the whole notion of running in the morning, had the husband take the girls at 6am when they woke up, and slept until just after 8am.  Ridiculous.

Why can't I sleep????  I don't get it.  Every time I know a long run is coming in the morning, I can't sleep.  It's getting horrible.  Should I just run some evening then?  Should I knock myself out with drugs?!??  This has got to stop!