Depression is a mental illness for many as its stress related which can lead to physical effects too. Depression is not just linked with brain chemistry, it isn't just physical illness otherwise everyone who has ever had it would be on meds evry day for the rest of their life. That isn't the case for everyone. As I said no one is right or wrong in how they view perceive depression or experience, deal with it, just differs a lot. Who said its due to chemical imbalance for sure..its more likely stress induced which can affects people mentally and physically. We have to be in control take charge if we are to liberate and transform. If not then we'll likely carry on staying stuck in difficult place or vulnerable. Some people have learnt to change their view of depression in a more helpful way to them and have been able to overcome it. Depression tells us something's wrong that needs attention , addressing and changing. A lot of people now are learning about how negative thoughts, beliefs and behaviours,unhelpful habits we have can lead to depression and anxiety issues. You can see this in different therapies or positive psychology courses/workshops on how to challenge and change way people percieve and respond/deal with things.