When I get up to run before work, it's basically an angel v. devil debate on my pillow. Angel says "Get up and go work out. You'll feel better and you won't have to worry about it tonight." Devil says "sleep in some more. You can always work out tonight after work."
And that's why I love Saturdays. I can sleep in AND still go run - usually much farther than I do on weekdays because I don't have to watch the clock to go get ready for work.