I'm a supporter here, not a sufferer, but I've suffered from severe depression all my life and I know the feeling you describe very well.
I wouldn't interpret it as "completely losing it." I think it's a self protection mechanism wherein your brain just had enough and needs to stop - emptiness is an okay feeling to have. What's most important during times like these, I've found, is to not over-interpret the feeling. There is something quite elemental and present about an "empty" feeling, and it's something to take note of, taste, experience, and just let be. The more we let our emotions be (or not be, in this case) as they are, the easier they will wax and wane. And the more we latch onto them, interpret them, resist them, the more they stick around and become our reality. With practice we can see how transient all our emotional states are - from emptiness to anxiety, happiness and joy. They come and go, disappear and return. Being able to relax with whatever emotional state we find ourselves in, observe it, make friends with it, and let it be is probably one of the most valuable things we can learn when dealing with depression and any "disorder."