I wouldn't say I get "depressed", so much as just mentally (and sometimes that seeps into the physical body) fatigued. If something keeps me from finishing something I was working on, or prolongs it, I get "depressed". Tired, rather. I feel as if my energy is just draining away.
Anything that requires social interaction tires me. I see that as a duty, or a job, that needs to be done. "I have to be social because others expect it of me and quote on quote normal people socialize". It's not that I want to - it's because I feel it is necessary. I'm always drained afterwards.
Even my job requires constant social interaction. As a service clerk, I have to bag groceries and take it out to the car for the customer. I have to talk to people the whole time. That really sucks out my energy. I'd much rather go clean the bathrooms or mop, or change a bottle bin, etc. Don't have to deal with people.
This isn't to say I'm not friendly -- I put up that facade every day at work. It's necessary. I smile and say friendly things. The rest of the time, though, I revert back to my comfortable blank expression and only speak when I have to.
I suppose I have said all that to say this:
Anything I see as a job, duty, or the like, *drains* my energy, therefore making me somewhat depressed.
In order to restore my energy, I need to have a good amount of "alone time". I need to go up into my room and spend some time immersed in an RPG, or a fantasy novel, or writing something, or making to-do lists. I generally cut off all social-ness for a bit.
Tonight, for example, a couple of my friends went bowling and invited me. I turned them down because I'm very tired, it's late, (Didn't get out of work until 10:00 PM), and I'd rather just be alone for a bit.
You other ISTJ's understand me, right?
Always remember to flank your enemies. History won't remember how dramatic your failed frontal assault looked. - Dragon Age: Origins