I can understand why you’re tired.
I do research on this topic everyday and work in a clinical setting. I find it fascinating and it really helps people to understand themselves. Been doing it for over 20 years.
It’s not entirely biochemical, nor is entirely free will/choice. There are many influencing factors including conscious awareness /subconscious, emotional/logical consciousness, perception formulation, and the resulting biochemistry. Bottom line though is that perception influences biochemistry as much or more than biochemistry influences perception.