Picture someone three weeks sober who can’t get out of bed. Cravings aren’t the main problem. The heaviness is. That story is far from rare. The 2022 National Survey on Drug Use and Health estimated that 21.5 million U.S. adults had both a mental illness and a substance use disorder in the same year. Mental health and addiction rehab exist for exactly this overlap. Below, we look at what dual diagnosis really means, how often it happens, what depression does to recovery, and which therapies and relationships help people stay well.