From WorldWit, some advice on what to do when you do land what you thought was your dream dayjob, and to your horror, you're finding you are second-guessing yourself:

You've landed what you thought was the job of your dreams. Each stage of the interview went smoothly - you sold them on your skills and expertise and your prospective boss sold you on the position and benefits of joining the company. She seemed excited about extending an offer. And then, with offer in hand, it was thrilling to give your notice (or tell your friends you're finally employed after a long stint of unemployment!). All seemed right with the world.

You've now been on board a few days...a week...perhaps even a month. Suddenly you're not so sure that you've made the right decision.