I have been living with chronic clinical depression since around the age of 15. I constantly cycle through depression, with depressive periods lasting anywhere from a couple of weeks to a couple of months. During these times, I struggle to stay awake for longer than a few hours, have little motivation to do anything, and feel despondent about my entire life. I struggle with these depressive periods several times a year, and while the symptoms have been lessened by antidepressants, they have not gone away.
Most people have periods of depression in their lives, but mine often happen from little to no external stimuli. I have typical depressive periods after times when I have been extremely stressed, like university semesters, but also become depressive at times when I have no irregular stressors in my life.