I was just wondering about this very same thing.

Sometimes in depression, I get stimulated by social interactions and become somewhat animated. I'm an extrovert so it makes sense that this can happen. But while I'm talking (usually babbling) and doing things, most people would be surprised to learn I'm depressed. I'm outgoing when this happens, but the entire time I feel it draining and I feel the dull pain inside.

I would describe this state as more agitation and anxiety than being up, but most people looking in wouldn't see that. They would see me talking, interacting and doing things. But it is VERY hard on me to force myself to do this and it takes a huge toll. While occasionally making myself go out and do something will lift my mood, more often it will make it worse and I crash hard when I get home to safety.

My depressions last for months and months but within that whole time I'm not always in bed. The depression itself has it's own cycle ranging from:

"I feel like garbage and I'm not enjoying anything but am able to drag myself around."

All the way down to "I can hardly move or talk and I don't see the point."

The months of depression are spent between those two depressed extremes.