[einpoklum]

I occasionally suffer from this pattern, although not as gravely as you describe it.

Something that I found helped me with the "bigger" manifestations of it, i.e. not a small homework assignment but larger projects in life, is: Stop psychologically evading failure.

That is, the instinct is to try not to think about what happens if you fail, since that's terrible; and maybe trying to convince yourself that you won't fail (and indeed maybe you're unlikely to fail). I say, do the opposite of that. Try to work through that worst-case scenario. This often brings up fears such as "What is my life about if I am unable to do XYZ?" Or "My self-perception is of a 'doer of X'; who am I, as a person, if I don't successfully do X?" If you are willing to face those questions and provide answers which you can conceivably live with, the fear of tackling X may subside somewhat.

Hope that helps.