I have, intensely. Yet I came to believe that the root cause (the external situation, real, perceived or otherwise) and the emotional reaction to it (self-doubt

I have, intensely. Yet I came to believe that the root cause (the external situation, real, perceived or otherwise) and the emotional reaction to it (self-doubt, depression, sense of failure) do not need to be intimately connected. In other words, your emotional health is not contingent upon your external circumstances to a large degree. To wit, a lot of very distinguished persons (as well as celebrities) battle very hard with the exact same feelings that you have. A lot of people in circumstances you might consider worse than yours (oh just watch a couple episodes of dirty jobs on discovery channel) are quite happy. Of course the reverse applies as well, but you can see how in the larger scheme of things, external circumstances do not dictate your emotions.