It’s a lack of feeling, you don’t really feel sad, happy, angry, etc. I think one of the biggest things a lot of people think of when they think of depression is it’s just being sad but it’s not really.
Really depression is the lack of everything that makes it interesting to live, to feel. You lack energy to do anything, and getting out of the hole feels monumental. Any small progress can then have you fall easily into the bottom of the hole after making any progress.
It’s also happens that it causes circular reasoning and continued re-emergence of questions that can’t be answered or you’ve already answered. Ruminating on thoughts leads to feeling tired mentally and physically and exacerbates the problem of depression, sending you further into the void, feeling even more emotionless.
Depressions greatest trick is to tell you that you can’t change anything, that you want to feel this way forever and unfortunately can lead to the worst scenario.