I would say my depression is extreme. I have "atypical depression", though, so it manifests a bit differently than melancholic depression. My moods are unstable, and I can feel happy and exuberant for a while during the day in response to some positive stimuli, only to be sobbing and fighting the impulse to ctb hours later. It sounds like bipolar, but it's not. Nor is it uncommon. It's a subtype of depression that's much more common in women for some reason.
The shifts in mood happen daily, throughout the day. It's exhausting and unpredictable. I have a hard time functioning smoothly in my daily life because I don't know when I'll be "happy" and when I'll crash into despair again and find myself unable to complete basic tasks because I can't stop crying or wishing I was dead. It's a rollercoaster. I haven't worked in almost 10 months because my depression is so destabilizing.
I don't think it's just brain chemistry that causes this. Personally, I believe my depression stemmed from childhood trauma and abuse. I don't know if it will be "cured". It's completely overtaken my life. Everyday is a struggle