More seriously, yes, "not starving" is part of the reason. But also, at least some days, there are things that I genuinely want to do. Sometimes there are problems at work that I want to solve, or things I want to get working. Sometimes there are people I want to see, or entertaining things that I want to do. Sometimes there are things around the house that I want to do, if only to get them out of my hair.
And if there's nothing that I need to do at work or at home, and nothing on the calendar? Well, there are things that I do for fun - I'll go do one of those.
On weekends - sometimes I don't get out of bed for most of Saturday... Just recuperating after 5 days of madness. Whenever do I have enough energy, I'm usually excited about exploring something - reading a new book, trying out a new video game, maybe cooking a new meal or finding new path for a walk around my home. But mostly, just the thought that this whole day is totally mine alone can set me into an excellent mood.
Seriously, though, was that a generic question, or are you feeling depressed/unmotivated?
I love my cats :)