You've probably heard of the doctrine of the Seven Deadly Sins, set out in paragraph 1866 of The Catechism of the Catholic Church. There is no direct Biblical source for this but the concept is apparently based on Proverbs 6:16 and expanded upon in Paul's Epistle to The Galatians 5:19. This is one of the aforementioned transgressions with which the Church berates its followers:
The deadliest sin, accidie (or acedia) is often mistranslated as Sloth, and interpreted as simple laziness. But the original definition is more complex. In modern terms, it is a combination of depression, distraction and despair which leads to the inability to do anything at all. I find that as St Paul said, I do not what I should and do what I should not. But why? I was reading about fear of failure and fear of success, but the roots are deeper.
Click on the link and read the whole article; it's just a couple of paragraphs and it will only take a couple of minutes. I think most of us have probably experienced this phenomenon to a greater or lesser extent and I doubt if we've got a proper explanation for it or, if we have, that it will be the same as anyone else's. Accidie often manifests itself as displacement activity - you find yourself doing something that you persuade yourself isn't a total waste of time when actually you've got plenty of stuff that ought to be done. But somehow, you don't want to get on and do it and you find excuses not to, then you get depressed because you haven't done it, and so forth. Eventually you reach a crisis. No doubt there are some smartypants out there who don't know what I'm talking about, which is probably a good thing, or whose reaction will be to say "Snap out of it and pull yourself together." But there you go.