In his book About Writing, British novelist Gareth L Powell devotes a chapter to THE FEAR, a ghost that haunts the life of many – if not all – writers, the Beastie on the back (to quote Jethro Tull) of those that do creative work.
Powell describes it thus…

We’ve all been there.
I was there, actually, no more than half an hour ago, as I reviewed the first part of Shadow of the Rat God, and concluded it’s the most worthless, useless pile of wasted words I ever put together.

But I’ve learned to expect THE FEAR, and not mind it more than it deserves.
It’s a sign, to me, that the story needs to be closed as fast as possible, because I am losing interest, and momentum.
Time to go that last mile.

Another bugbear I’ve been acquainted with these last three years, and one that is a lot harder to shake off, is what I might call THE VOID, and it’s something that usually hits me during the weekend, when the dead place in which I live is even more dead than usual, and the sense of futility becomes overwhelming.
THE VOID is cognate to THE FEAR, because they both hinge on a sense of uselessness and futility, but THE VOID is a lot more personal.
If THE FEAR tries to suggest you that all you are doing is worthless because you are a fraud, THE VOID works on the fact that it does not really matter. To the contrary, you are actually quite good, but it does not count for nothing anyway.
Nobody will read your next story.
You are alone.
Forever.
It does not matter how hard you work, how much you try to improve your skills, how much effort you spend.
It will all come to nothing.

Escaping the spiral of self-pity and depression is not easy, because it comes with a sense of fatigue that makes even standing up from the computer a torture. And then, you rise from the PC, and where do you go?
There is nothing, but the emptiness of the Void.
It can become soul-shattering.

I usually counter by listening to music, or by watching an old movie, or chatting with friends through the web.
But it’s a dark and cruel Beastie, THE VOID, and it can really give you a hard time.