Fellas - please note that I made it clear it was a guess. That is all it can be; and not even an informed one. A well intended one? You bet. Other than that it is a crap shoot.
I'll share a little more info with you than I normally would: I went through something about 8 years ago that really seriously took a toll on me. BP went through the roof. Night sweats. Waking up every hour or so. Literally - I was a nervous wreck. I felt like I had the living hell beat out of me 7X24. I won't go into what caused it, but it wasn't trivial.
I agree a dramatic change in schedule can throw you for a loop. I didn't read into your post that it was a new change. My bad if it was there. Although I did overlook the 12 hour days. But IT IS POSSIBLE THAT the schedule may not be enough and here is why I say that: When I went to grad school, I was working (mangemet position) full time, remodeling a house, 2 kids and finished the MBA program in 3 years (not the normally scheduled 4). So, I was fairly sleep deprived. This isn't about me, so why the heck am including this? None of that resulted in depression - for me - under those circumstances. Your circumstances may be entirely different' possibly far worse (again, I would have no way of knowing).
What later caused depression was emotional, and really rocked my foundation.
As to meds: Paxil, for me - was a blessing. Without it, I was barely able to function. Believe me, I tried to tough it out, tried herbal alternatives, etc. It simply didn't work. The Paxil did. It is magic? No. Did I like the idea of taking it? Hell no. Do I like taking any kind of meds - no, not at all. Did I use it when I needed it most. Yes. BTW - it can have some crappy effects when weening off it.
Re meds part II: Please take a second look at what I said: "Also, don't be too leery of using the meds. They can help while you work on the root cause." Why did I say that? Honestly, there is a huge and unnecessary stigma about depression and antidepressants. People sometimes avoid taking them because they believe doing so is a sign of weakness or they believe they should be tough enough not to have to rely on them. Properly administered, in small dosages via a competent MD that understands what in the heck I going on with you, and with an appropriate feedback loop, antidepressants are not inherently evil. I would not make the same claim of all meds (e.g., painkillers). I’ll say this – you are far better off with something designed to help you than you would be by pounding down some drinks (depression + depressants = not good).
As was rightfully pointed out, depression - if indeed that is what you have - is a chemical imbalance. Just as with other types of imbalance or dysfunctional balance, it isn't going to magically change without something to cause that change. That change may result from your body adjusting to modified sleep patterns (it is actually far more than this, and there is a great deal of literature available to help you out). On the other hand - if it isn't sleep related, then you might want to look at other alternatives.
Guys - I truly went out of my way to offer what was clearly stated as a guess. Take a look at it again: “BTW - I would guess it isn't your job - frequently it stems from anger or resentment.”
I said this for a couple of reasons. First – this has been my experience, and the experience of most of those I’ve spoken with. Secondly - as guys, we are likely to be less willing to look at our “hurts” for a variety of reasons (including not wanting to look like a puss). So, we might be more inclined to look for more logical causes – like work. Make no mistake about it work can be the cause. But there may be a variety of other causes if that isn’t the cause (or if work is only one of many causes). One source of information on depressions says the following: “A serious loss, chronic illness, relationship problems, work stress, family crisis, financial setback, or any unwelcome life change can trigger a depressive episode. Very often, a combination of biological, psychological, and environmental factors are involved in the development of depressive disorders, as well as other psychological problems.” Maybe it is just me, but I see that as being one very one broad list.
Why take time to respond? A couple of the responses to my earlier posting seem to suggest that I was saying that it couldn't be work related. Heck, of course it can.
Look - I'm just some slug willing to offer an opinion/guess based on my experience. Again, there isn't any way that any one of us who took the time to respond can give you anything definitive; although I wish we could.