You know that sickening feeling of inadequacy and over-exposure you feel when you look upon your own empurpled prose? Relax into the awareness that this ghastly sensation will never, ever leave you, no matter how successful and publicly lauded you become. It is intrinsic to the real business of writing and should be cherished.
Don't panic. Midway through writing a novel, I have regularly experienced moments of bowel-curdling terror, as I contemplate the drivel on the screen before me and see beyond it, in quick succession, the derisive reviews, the friends' embarrassment, the failing career, the dwindling income, the repossessed house, the divorce . . . Working doggedly on through crises like these, however, has always got me there in the end. Leaving the desk for a while can help. Talking the problem through can help me recall what I was trying to achieve before I got stuck. Going for a long walk almost always gets me thinking about my manuscript in a slightly new way. And if all else fails, there's prayer. St. Francis de Sales, the patron saint of writers, has often helped me out in a crisis. If you want to spread your net more widely, you could try appealing to Calliope, the muse of epic poetry, too.