I know that the "chemical imbalance" explanation is a poor excuse for "we don't know exactly how it works". But there are so many progresses done in our quality of living that were done because someone had a hunch and some practical, reproducible results showing that it worked. Think about the practice of washing hands when going from one patient to another in a hospital? When it was suggested, people couldn't see a connection with dirty hands and spreading diseases.
I lost a son that suffered from a mood disorder to suicide. It is heartbreaking and it happened when he was apparently getting over the hump of his darkest moments... I have other two children that also struggled with depression and what I found that worked the best for us so far is communication. Being opened about our struggles, talk therapy in conjunction with medication.