Ashoka
श्री कृष्णा शरणं मम
You don't know the reason why you are depressed? What causes the "chemical imbalance"? I would like to hear, what it means to you to be depressed.
It really doesn't matter what it means to me. What matters is what it is; a disorder. Just as substance use is a disorder.
For a person with substance use disorder, they, at first, use the drug to experience a high. That high releases chemicals like dopamine and serotonin at high levels. But eventually, you develop dependence, and the levels you are seeking of these chemicals is higher and higher. Eventually, you are using, not to feel a high, but to feel normal.
Post Acute Withdrawal Syndrome occurs when a person stops using; the brain forgets how to make the "happy" chemicals and needs to relearn. But this can take a while. So, you will have feelings of irritability, depression, fatigue, among other things. Because your brain is learning to make the chemicals by itself again, rather than being reliant on a substance.
With depression, the brain doesn't make those chemicals, or enough of them. Which is why we have SSRI's and other medications to help with making those chemicals. It's actually very common for people, who have substance use disorder, to have a comorbid diagnosis of depression. Others include anxiety, PTSD, and chronic pain.