What is this feeling of Inertia about and how to change it?

“Inertia is the resistance of any physical object to any change in its state of motion, including changes to its speed and direction. It is the tendency of objects to keep moving in a straight line at constant velocity.”

A little background. I am a self-employed artist and I have a lot to do at the moment. Indeed a long list of things to do. In recent weeks I have felt invigorated and active; I’ve been to meetings, painted a lot, developed ideas, felt buoyant and inspired, energetic even.

This week I have spent a lot of time at home but have this feeling of inertia, I can’t get going..I know I have a lot to do, but something is holding me back. It could simply be tiredness I guess…I feel exhausted, my body aches, my joints hurt. But I also feel rather down, listless, demotivated, hopeless. I have an overwhelming feeling of simply not being able to start anything or finish things that I’ve started. I sit at my desk and think “right! I’ll do that” and I feel a tendency to close my eyes and run away or do something else (like Fluther!)

Do get these kind of feelings of inertia?
What do you do about them?
Is there a psychological resistance to something do you think?