The "dark night of the soul" is a spiritual concept describing a period of deep spiritual crisis, while mental illness is a medical condition affecting mood, thinking, and behavior. While they can share similar symptoms like deep sadness or existential questioning, they are distinct experiences. A dark night of the soul doesn't necessarily trigger mental illness, nor does mental illness always lead to a spiritual crisis. However, they can coexist or influence each other. The intense emotions and questioning during a dark night of the soul might exacerbate existing mental health issues, or the struggle with mental illness might prompt spiritual questioning. It's crucial to address both spiritual and mental health needs, potentially with different approaches.