I've personally experienced the depression following all 3 of my open heart surgeries. Fortunately, the docs and nurses warned me that it was probably going to happen and to just ride it out knowing it would go away. I think it lasted about 6 weeks with me. So, after the next 2 open hearts I knew to expect it. In talking with many people who have gone through open surgeries, I've found that this is not often discussed prior to the surgery. I'm going through it right now after having my 11 stent placed in my heart in January. It's different than the "after open heart depression" but nonetheless, still very real.
I'm just trying to "ride it out" hoping it will pass soon. I fortunately have a very loving, supportive wife that has been my sounding board.