I think.... mindfulness is being aware of the moment you are in and not thinking about the future or past just then.

Hmm since I suffer from winter depression too, I have to admit I can't see a link myself between winter driving and mindfulness. However... since I am mindful that grey days make lots of people feel low, maybe you could use that mindfulness to create a bright room you can cheer yourself in? A fire, maybe? Some hot coffee or soup... favourite music, good book... just sit and take in a moment being mindful of some good things?

And as for the guilt... well, it need not be for hours. Just long enough to drink a drink or listen to one cd or for a time period you set. After all, it is for your health. No need to feel guilty about that