In the meantime, I direct you to this wonderful post by Rands. Read that and tell me that isn't what you experience every few years. :) This is quite possibly the biggest reason why it's so dang hard to be consistently good. After a while, you get bored and lose your sense of purpose, and you wonder, "Just what am I doing with my life?" Which is also perhaps exactly why your sense of purpose and raison d'etre should not come from your work, even though work will consume a good portion of your life.
Sit back and reflect on what gives you purpose. Whenever I got stuck in life, I never felt like I could really depend on family or friends to pull me out of whatever pit in which I was sinking. I just never felt like they "got me", with the exception of a select few. I could only pray to God, struggle forward, and go for long walks at night. There was this big huge tree near my home, and I'd go stand by it and just stare upward.
Somehow seeing how small I was compared to that tree, and then seeing how small that tree was in comparison with the universe that shone above, made me realize that no matter what happened, it didn't matter too much. It was then that I could start to laugh at myself and just move forward. Big results, small results, successes, failures, just have fun with it and be at peace with it. Life is too short to be stressed or depressed about insignificant things. But every now and then, you really do want a significant big change, just as Rands is describing.
OK, your back's up against the wall and you can't live another day without emotionally vomiting? Then go do something, have fun with it, don't just sit there complaining. Serendipity can be wonderful for that. Unfortunate for you if you (or your significant other) can't stomach the risk.
When I Have Fears that I May Cease to Be
By John Keats
When I have fears that I may cease to be
Before my pen has gleaned my teeming brain,
Before high-pilèd books, in charact'ry,
Hold like rich garners the full-ripened grain;
When I behold, upon the night's starred face,
Huge cloudy symbols of a high romance,
And think that I may never live to trace,
Their shadows, with the magic hand of chance;
And when I feel, fair creature of an hour
That I shall never look upon thee more,
Never have relish in the faery power
Of unreflecting love;--then on the shore
Of the wide world I stand alone, and think,
Till Love and Fame to nothingness do sink.