How to Loosen Up

Dear Books, I have a hard time loosening up. I feel like I’m coiled into a ball of string, with tight movements, short breaths, a fear of dancing freely. I’ve made an effort to loosen up in some areas of my life with reasonably good success (notably: parenting; I don’t want my daughter to bear the ill effects of my inflexibility, so she gets the less uptight version of me. Usually). How do I allow more air in my lungs and more movement in my arms and, I guess, less fear in my overall sense of self?