Yeah there are two different types of depression. I am not talking about the snoopy and charlie brown, guy with the blanket and clouds over his head.
I am talking about clinical depression. It is more along the lines of low functioning.
Nobody wakes up in the morning and says, hey, I feel 10 IQ points lower today.
I've been poisoned in the past. It is almost entirely non-perceptible. It wasn't until I started trying to draw stuff that I knew, something had seriously fucked me up. I started trying to time how long it took me to do simple math like subtraction, multiplication, division and addition. Some of it was simply impossible for me at the time.
Something can hit your brain anywhere really and mess it up. There are different parts of the brain responsible for different things. You are pointing out muted emotions, but your behaviors and speech are saying something different if you ask me. You are acting if you have guilt and fear, and such, you just are not feeling the way you could be. You are dead inside, just a touch... possibly clinically depressed, the low functioning variety...
See the key difference is that someone can also be depressed, and feel deeply sad. That's the charlie brown variety...
To give you an idea of how common clinical depression is... think of the thousands of toxic dangers in our society. You could have carbon monoxide leaking in your friggin basement and be doing brain damage every day, and have no clue what was happening.