I have been trying to figure this out for the last five years. Its always been an effort for me to get out of bed early, esp. on a holiday, for my run. Yes, there are some days when I am highly motivated & I can manage it, but on most other days its a very big effort. Everything else has becomes a habit/routine, but not this thing. I am a early morning person and am at my productive best in the mornings, but I still have not been able to figure of why its so difficult, other than the two core facts that I love my sleep (I can sleep anywhere and at any time, especially in a moving vehicle or while waiting for something/someone. This is a big plus under normal conditions, as I can easily nap any time and be really fresh for something important, plus I don't waste time doing nothing!!) and the second is that fact that I am extremely lazy (so doing something that I don't enjoy is a big effort). Another special trait - if I have had a hard week with limited sleep and I want to make up for it on a Sunday, I can easily get up in the morning, have my breakfast and go back to sleep (can't sleep long hours on a empty stomach).
Now the solution, this has been arrived at after years of research. I have tried everything from changing into my running gear as soon as I get up, to immediately brushing my teeth on waking up, to doing stretches after getting up, to switching on the TV or loud music,...... the list goes on, but I always manage to laze around for a long while or actually get knocked off to sleep even in a sitting position. Today I got up and immediately went for a shower, this made all the usual issues/problems just disappear (the reason I have never tried having a shower in the morning before a run, is the fact that I need to have one after the run and it did not make sense to have two showers in quick succession). So, from now on I plan to have a shower before my run on all holidays, so that I can have a early start and beat the sun (the rains are almost over and sunny days are back!)