Great observation Pongomp! You are definitely not alone. However, I don't think that what your feeling is limited to your weight loss.
I think that it's more about goals and direction. I believe that you are a goal oriented person. For so long it has been your goal to lose weight. You have put tremendous amounts of time, money, effort and focus into reaching that goal. Reaching that goal has somewhat consumed your existence.
Now that you've reached that Goal comes the question "Now What?"
I'm just starting my Weight Loss Journey and pray to be where you are one day but yet and still I can totally relate.
I've always wanted to be a lawyer since 6th grade. I did contest in highschool, I went to undergrad, I took prep classes for the LSAT, I took the LSAT, I applied to several law schools, I got accepted to Law School, I attended law school, I got a job with a law firm, I graduated from law school, I passed the bar and now I'm a full fledge lawyer.
I am extremely grateful for the blessing I've received but at the same time I've had a the "now what momement" I think that what we both have to do is set new goals and continue the cycle for the rest of our lives. Goals help you stay focused and reaching them is one of the greatest pleasures we have.