This is very common, Tammie. It happens to me all the time. I prepare myself now to be depressed when good things happen to me. At first I´m numb, then sad and it takes about 3-5 weeks to feel better.
I try yoga and positive self-talk. I try to tell myself I deserve it, but the negative voice in my head has pre-programmed me and it takes all I can do to just accept my sadness. But it passes, and this I know.
When I worked in the mental hospitals as a student, some people were hospitalized because they had won lotery tickets, a huge amount. They had been struggling all their life and all of a sudden they could do what they liked. I thought this so bizarre, but the doctor explained to me it´s a big stress factor to get good things in your life, especially if you´re vulnerable and have been struggling. On the stress scale over here, it accounts for 20% (divorce being 80%) and I´m talking normal people, not bi-polaire.