If writing is your profession, then "mood" and "whether you feel like it" are irrelevant. Do you take time off work because you just "don't feel like it today" - well, you better not do it too often or you'll be in deep doo-doo.
I have been known to say this on a number of occasions, of course it's harder when it's yourself.
Personally if I take a day off from the day job I don't get paid because I'm a contractor. That's a fairly convincing argument. Luckily I can also work from home which has meant that the snow preventing me from travelling to Sheffield (all the Pennine passes have been closed) hasn't stopped me from working.
What brought this on? Well I really didn't feel like writing today: sleepy tired, and me old bones a bit achy. But I have less than two episodes of Winter to write and they need to get done. (Then there's re-writing, getting 3rd party analysis and critique, then working with the Director - Hi, Chris - and shooting in just a few of months.)
So I forced myself to sit down in my office in front of the computer and start writing.
You know what? I feel so much better for it. Getting things done does wonders for the way you feel.
EDIT: Couple of hours later - first draft of Winter is now complete and printing, for typographical and sanity check. (I deliberately changed some things halfway through, now I need to make sure the beginning agrees with the end.)
What's on the turntable? "Preludes" by Gordon Giltrap from "The River Sessions"