Generally it is seen as an illness if it adversely affects the person's ability to function day-to-day. Its one of the reasons why homosexuality was proven not be a mental illness in the 1970s and stuck off from the DSM.
From a person with depression it does affect me day-to-day sometimes I have to be forced to get up by my boyfriend since I don't feel like its worth it, sometimes I can't go through the day without needing to cry and hurt myself over nothing, I am irritable, don't eat well etc. thats an illness.
From a person with depression it does affect me day-to-day sometimes I have to be forced to get up by my boyfriend since I don't feel like its worth it, sometimes I can't go through the day without needing to cry and hurt myself over nothing, I am irritable, don't eat well etc. thats an illness.