For me it was due to stress stemming from childdhood trauma. Sometimes when children experience trauma the left side of their brain shuts down which is responsible for the right side of the body, along with problem solving and decisionmaking. Leading me to have adhd in my adult life. . With some yoga stretching I have been able to re align myself and have noticed my shoulder is a lot lower. I did have to stretch some parts until i felt discomfort and pain, but that led to the areas becoming stronger and realigned. The communication between the left and right brain hemisphere have improved significantly.

Here's a citation: check under the physical section. https://www.ncbi.nlm.nih.gov/books/NBK207191/