Is this the case for anyone else?

There's always at least one day a week where all I can get myself to do is stare blankly at my computer at work.
Ok. I'm exaggerating. I can get myself to go on facebook, check my newsfeed 8 times, read NYTimes articles, write journal entries. Oh and Ooo! Ooo! I can get myself to read budgeting articles and material for clients. But anything beyond sitting here and reading becomes incredibly difficult.
This week that day is Monday. I've been sitting here, reading the Budgeting Workbook, slowly but surely. And although I feel lethargic because of the great feast at my family's house yesterday, I have a feeling that this has to do with more than my physical health. It's probably indicative of what I'm meant to be doing.
I'm reluctant to say that I'm meant to be in a work environment where I can be writing, reflecting, reading and conceptualizing. But I'm finding that, in this environment, those activities come the most naturally.
So the question becomes, What to do? Another important question to ask might be, What is the nature of these unproductive days? It it just a case of the Mondays? Is it my job or is it me (i.e. should I be looking to change some sort of thinking pattern or habit that will cause me have a case of the Mondays every week no matter what job I find myself in)?
Perhaps, I'll leave here at the end of my assignment having written a novel about my clients, their stories and anecdotal information on best practices. I'll call it: Poverty and Social Service Agencies: From the Eyes of an Observer on the Inside.