First time I've seen this mentioned somewhere...I've lived with depression for several years, and exhibit a lot of sociopathic behavior. The only thing is, I'm very emotional also, so I consider myself a borderline.
It's probably one of the most entertaining combinations to have..but I always find myself wishing I was just full-blown socio, so I could be more functional..haha
They are undeniably related. Push someone far enough, and the only healthy response would be voiding all emotion, because it's just too costly.
Clinical depression and beyond such as Major Depressive disorder is more of a mood type situation. While regular depression is more of a sadness or emotion per-say. This is what I have researched and developed together.
Think of Blue's music as regular depression/sadness. Now think about Depressive Suicidal Black Metal (DSBM) that is more of a severe mood disorder. If you are at that stage in depression I am pretty sure regular sadness or guilt for others is extremely slim.
ex.
Regular Depression-Sadness
Clinical Depression/Major Depression-Emptyness