Can I reclaim lost personality traits?

When I was a kid (probably until the age of about 12 or 13), my personality had a strong 'I' element (as in the DISC model I). I was fun, energetic and confident. I was willing to express myself openly (and loudly) and do silly things for the sake of laughs. When I went to high school, I was bullied heavily. I became much more quiet and withdrawn. The C element of my personality took over, and the I element all but disappeared. Now as an adult, I would like to be able to "reclaim" my lost personality. I am generally a shy and withdrawn person, and I long for the energy and enthusiasm that I once had. Is it possible to reclaim my lost personality? If so, how?