A gentle but steady current of anger inwardly directed will result in depression over time. Many people experiencing depression are surprised when mental health professionals question them about anger. Are you angry? Where is your anger? How are you angry? Can you express your anger, share it, verbalize it? Sometime is requires a substantial amount of cognitive, emotional, and spiritual spade work to uncover and expose this well of inwardly-directed anger.
Everyone is familiar with anger that explodes. But anger that seethes can be just as dangerous. Particularly when we are the targets of our own quiet rage.