Anyone every experience this: you work so hard to achieve a certain goal and then when you finally "arrive" you lose interest?

I have two examples. For the last 2 years I really wanted to race Expert mountain bike. I trained hard, lost a couple of pounds and finally placed at a race in Expert Cat--against a decent size, competitive field of women. I thought that would motivate me to train and work harder to improve beyond that. But since that point last fall, I've lost interest. Now that I know I can do it, I don't feel like I need to anymore. As much as I try to rouse my motivation, I can't. I don't know if I even want to race anymore.

Example 2: Since I began my design career 14 years ago (while I was still in college) all I wanted to do was advance to Art Director position and concept Book covers. It took awhile, but I recently got the promotion I've wanted for almost half my life. And now that I'm here, I find myself scanning the want ads and looking for not only a new job but a career change all together!

What is WRONG with me? And I even enjoy Art Directing! Agh! I'm screwed up in the head.