We often talk about biochemical states as causing affective states, but maybe they're really the same thing.
It's not uncommon to hear framings like "the depression was caused by a biochemical imbalance" or the "hyperthyroidism causes fatigue", but I think this reflects a sort of mind-body dichotomy that undermines our ability to understand the true causality and relationships between different aspects of things in reality.
I'm not suggesting that it's always wrong to think in these sorts of A causes B terms. But often, I think it leads us to miss that sometimes A and B are actually just different perspectives on the same fundamental phenomenon. For example, in some cases, the depression is a biochemical imbalance; the particular brand of fatigue a person is experiencing is hyperthyroidism.
This is fundamentally consistent with my view that the mind / consciousness (and our affective, experiential states) is an action performed by the brain (the physical matter). Loosely, you can think of the mind as an emergent property of the brain. I think it's weird to say that legs cause running. Legs do running. The legs moving in a particular way is running. The brain configured in a particular way and the chemicals whizzing around in a particular way is some affective state, such as depression. I think this is basically what it means to say that The Body Keeps the Score.
What I think is helpful about this way of looking at psychological phenomena (and really, a lot of other medical issues) is that it helps us to search for true causality, not think that we've understood the cause by describing it in biochemical terms. We haven't necessarily explained depression by understanding the chemicals involved, even though we have increased our understanding of the phenomenon. It's like color: Color is different frequencies of light; different frequencies of light don't cause color. Frequencies and the experience of color are just two different perspectives on or aspects of the same phenomenon in reality. (And this is true of our understanding of any phenomenon in reality: Our senses offer a particular perspective on that phenomenon, and we integrate different senses and different items of data into a more and more robust understanding over time.)
One of the pitfalls of things like "a biochemical imbalance causes depression" or "hyperthyroidism causes fatigue" is that it can fool us into thinking that the root cause is just biochemical, so we can address that (and thus we're not "merely treating symptoms"); it undermines the desire to look deeper. So we pop a pill, acutely or chronically, thinking that the biochemical state is just some irreducible primary. In many cases, then, we've actually just treated symptoms while fooling ourselves into thinking we've treated root causes.
Emphatically, I'm not saying that pharmacological intervention for a biochemical state is always wrong. But I think that there a lot of cases where a more nuanced and thoughtful approach would be beneficial.
For example, if I am depressed or have hyperthyroidism, and I just pop a pill, it enables me to continue the same behaviors that might have led to the depression or hyperthyroidism in the first place, further increasing my dependence on drugs.
Maybe my biochemical state is a result of life circumstances (eg, acute work stress or the end of a relationship) or lifestyle choices (eg, a sedentary lifestyle or ignoring pain while lifting weights) or even my own prior biochemical interference (eg, by taking too much of certain supplement or combinations thereof). These are the sorts of things it can be useful to uncover, and it could represent a true causal understanding of conditions. By addressing the actual cause, we might resolve the condition, which would be reflected in the affective and biochemical states, since those are both aspects of the same phenomenon.