It does get pretty tiring explaining the difference between them. Mine is definitely biologically based, although stress exacerbates it like it does many other things like acne. My "eureka" moment came in high school (when brain chemistry changes from puberty can cause such issues). I was at home playing video games online with friends when I noticed my vision was blurry. I went to the bathroom and saw tears streaming down my face, which baffled me as my conscious thoughts were in no way sad/negative at the time. There was just an underlying feeling of heartache. Over the next 4-5 years I worked with a professional and finally managed to find a drug combo that balances me out. I still get sad, but only for logical reasons, and only as much as I used to before my symptoms developed. It has been a full year for me now without any "episodes", something I had not thought possible previously. I just figured I would share this in case someone else might benefit from reading it.