Clinical depression, if diagnosed by a medical professional, is a qualifier for disability. That, and if you are taking any narcotic-containing prescriptions, usually limits one's ability to maintain any meaningful employment. So sorry, but you aren't by yourself. Depression is a crippling illness suffered by millions!
It comes with inability to concentrate, memory loss, so many things. Disability will rely more on your physician's statement than yours. Many people who are depressed cannot stay awake. That is an automatic disability!