Cutting. self mutalation?

if a person self inflicts pain and causes bleeding to oneself what do you suggest that person should do to get help? or is that a common stress depression etc reliever? its not a suicide attempt! and not for attention. the scars are minor enough to prevent scaring or getting attention brought to. just need some advice. and what causes sudden depression for weeks at a time out of nowhere and then goes away for awhile? whats wrong?