When you're feeling sad consider the sadness to be a time to check in with yourself. Checking in with yourself are moments of reflection time; mirror, mirror, inside of me what are you telling me? I can get to the bottom of the sadness (root cause) when I take time to feel and become acquainted with my feelings. Becoming acquainted with our feelings is necessary because when I feel I understand what to do and what not to do? Example: I put my hand on a hot stove.
Reflecting on the inner thoughts and memories are something we all experience. At times we are reflecting on memories unaware of our thoughts, which means we create loops in our lives. The loop is replaying the same situation over and over. Moreover, self-reflection is a process that can bring healing when reflection is understood. When thinking on the memories that are unproductive, identify with the thoughts and shift your thoughts to the opposite which would be productive or healthy thoughts.
Example: Whenever sadness comes up reflect on why am I feeling this way. Then look, do, read, or affirm things that make you happy! The opposite of sad is happy! https://youtu.be/7nEaw4skfIU