Depression is serious business. DO NOT make the mistake of underestimating it.
A big effect is filling your head with false data, making you prioritize false data over true, failing to notice accurate data, or reach wrong conclusions from good data. This goes well beyond "the glass is half empty". It's more like "why doesn't she like me" when she does.
This can hugely affect your performance in life and job. If your job is doing doing orbital insertion trajectories - sure, you can probably still get good answers because that is pure hard science with one answer. But what if your job is counseling students on career paths?
This endless stream of data lies to you so effectively, and seems so real in key moments. You have to constantly bust the game: "No, it's not too late to go." "No, it's not the economy." And you must always, scrupulously search for facts that are more accurate than the facts you "know".
This is a human condition, and it's not just a brain defect. The human brain is optimized for one thing. And it ain't happiness.
Frankly, internal lying isn't just for depressed people; there's little regard for truth these days in politics for instance.
More than "tell the truth and keep your word".
It's about operating from a foundation of truth. When you have a squabble with a coworker and it's all their fault but it's actually kinda your fault on several fronts... you need to be cognizant of that in an accurate way.
When you are wrong, you need to know exactly what areas you are wrong, and exactly what areas you are not. This is to stop allowing depression to reduce it to "well I'm just terrible". It's so you can own up to consequences -- and can learn from, and change, the right things. Otherwise you don't know what went wrong, consequences seem arbitrary and random, which is very frustrating... you try to correct in all the wrong ways, it doesn't work, and it makes you frightened to try anything at all.
Don't just aim for normal
You need to train a lot to break bad habits or make good ones. Counseling is nice, but you can't seriously expect to make material improvements working 1 hour a week out of 168. That means following counselor advice the rest of your time. Structure can help a lot with depression.
I had the opportunity to work with very brilliant and productive people. The habits they recommend sounded like what counselors recommend! I arrived at a theory: Imagine a scale of 1 to 10.
Very Depressed Normal Extremely effective
A counselor isn't trying to make you powerful. She is aiming for "5", and is used to "settling in" for a long slow journey. Visionary people and life coaches are aiming for "10", and want to get you there as fast as possible.
The physical world
Of course it's not as simple as that. Counselors have a lot of tools specifically to treat depression that high achievers/coaches don't have. Not least, medical treatments. The people working in that field are very proud of their work, but they're just scratching the surface of what there is to learn. For instance, there is no brain-scan, DNA analysis or blood test to determine which of several SSRI's will be effective for you (if any at all). It is guesswork and observation.
Traditional or alternative medical practices such as traditional Chinese medicine sometimes have solutions, and usually can't hurt and might help.
Separate from that, mind conditioning such as meditation is extremely helpful, as the training quells the chatty stream of consciousness that every mind creates. Having your mind be able to be still helps a lot.
A variation are mindful body-exercises such as Yoga or Qi Gong or Tai Chi (as kundalini exercise) -- of course, you must do the mind part of the exercise, it defeats the purpose to wave your arms around, fail to run the energy, and let mind run amok on daily frustrations.
An even more honest variation are internal martial arts such as Tai Chi (as martial art), Ba Qua or Aikido which do not rely on raw strength but are powered by mindfulness and awareness. It tests your focus and discipline very honestly - either you succeed in tests or sparring, or you don't.
Even separate from that, physical exercise for cardiovascular health and toning of muscles is helpful.
Have a plan/vision
A great curse of modern living is our brain no longer has much to do. Our forebears have built this great society, where food, water, shelter, the core necessities for survival, are readily achievable for almost everyone. So what next? Minds abhor idling.
Many visions of utopian societies call for human beings following higher pursuits - as thinkers, artists, technologists -- life is supposed to be easy. Unfortunately nobody really shepherds us into that. Well, actually a lot of people do, and all the most prominent are selling "opiates of the mind" - television, Facebook, TV Tropes, World of Warcraft, the liquor store. They make shockingly small amounts of money by sucking you in - they call it "engagement".
A master plan for your life tears you away from those very cheap distractions and puts you on focus. If you work with a counselor or life coach, it also gives you clear benchmarks to aim for and hit.
Depression is hard. You can't just snap your fingers and not be depressed. You have to work really hard to overcome medical influences, self-defeating thinking, habits and distractions. A lot is just doing the right thing anyway - as I've heard it said, "fake it til you make it".
Back to that job
It's easy to think of a job as only being to supply your life needs. If you think in a highly accountable (and a bit American) way, you realize that for your employer, a job is actually about creating economic value for the company. You figure first there's your salary (duh). In western economies, benefits, taxes and employee costs (management, HR) can be as much as your salary (more if you're underpaid). That much again for the infrastructure cost of your workplace, desk, computer, network it's on, security, reception, you name it. So rule of thumb: you must bring in 3x your salary in bookable revenue for employing you to make any sense at all. Realistically a company won't survive unless a lot of employees are bringing in 10X.
So ask yourself: For this company, how can I increase my value and indispensability? What can I do to either bring in a lot of revenue, or show how I already am (without lying)? And an employer is a great framework in which to perform new skills and accountability.
Ultimately your boss doesn't care about sick days, he "dumbed it down" for you. What he cares about is bookable revenue: your actions creating wealth for the company.