It wasn't a philosophical problem for me. It wasn't that my value system was distorted, it was that my entire experience of existing was distorted. I could logically affirm that positive experiences are possible all I wanted, but they were somehow profoundly remote, in a parallel universe that I could vaguely remember but no longer existed in. It's not just that I had confirmation bias and fewer positive experiences, it's that my entire perception of everything -- every thought, every experience, every future possibility -- was so warped that positive experiences seemed like an impossible fantasy. More than once, I overcame a tremendous amount of lethargy and pessimism and tried to have a positive experience, and I simply couldn't experience it as positive, no matter how good it "should" have been.
That is the power of having a seriously screwed up brain. My symptoms improved not with antidepressants or psychotherapy or self-help, but with treatment for a previously undiagnosed chronic physiological condition. Despite having a "real illness", I've found validation for most of my experiences in first-hand accounts of people with "mental illness" (which is defined in such a way that the practical definition is "any psychological symptoms not explained by a lab test known to your GP"). Allie Brosh was mentioned by another commenter, and I definitely had a "holy crap, someone else gets it" moment when reading her "Adventures in Depression" comics.
(I'm being a little vague here, but given the still-extant stigma around "mental illness" and the amount of data collection that is now commonplace, I'm a bit paranoid about revealing enough to identify myself even under a throwaway account)
After ~20 years of on-and-off psychiatric treatment (some fairly intensive, some not, none especially effective), I found a psychiatrist with enough sense to strongly recommend that I get the relevant lab test. He had to tell me to request it from my primary care doc, because according to the worldview of American health insurance a psychiatrist is not qualified to order said lab test. My primary care doc gave me a questionnaire. My score was just below the threshold where the lab test is considered warranted. He told me he'd figure out how to make it work. I guess he did, because I got the test, got it interpreted by ${DOMAIN_EXPERT}, and got a prescription for treatment that seems to be working pretty well (albeit not perfectly).
That is the power of having a seriously screwed up brain. My symptoms improved not with antidepressants or psychotherapy or self-help, but with treatment for a previously undiagnosed chronic physiological condition. Despite having a "real illness", I've found validation for most of my experiences in first-hand accounts of people with "mental illness" (which is defined in such a way that the practical definition is "any psychological symptoms not explained by a lab test known to your GP"). Allie Brosh was mentioned by another commenter, and I definitely had a "holy crap, someone else gets it" moment when reading her "Adventures in Depression" comics.