Interesting show on Schopenhauer.
Here is a way of thinking about our commonsense asymmetric attitudes toward prenatal and posthumous nonexistence. Lucretius' "mirror-image" claim seems plausible if you think of these periods purely negatively, just as experiential nothingness. But if you think of them "relationally", i.e., as experiential blanks that are deprivations of the goods of life, then one can understand the commonsense asymmetry in our attitudes as a special case of the commonsense preference that, other things equal, our pleasures be in the future. That is, holding everything else fixed, I prefer my pleasures in the future rather than the past, just as I prefer my pains in the past rather than the future. Since death deprives me of future pleasures whereas prenatal nonexistence does not, it is not surprising or irrational that I care more about my death than my prenatal nonexistence.
For an early sketch of this idea, which builds on thought-experiments of Derek Parfit, see Anthony Brueckner and John Martin Fischer, "Why Is Death Bad?", originally in Philosophical Studies, and reprinted in Fischer, ed., THE METAPHYSICS OF DEATH, Stanford University Press.
A small point about pessimism: typically it seems to function at least in part as a defense mechanism, seeking to protect the individual from disappointment. This of course resonates with the Buddhist idea of reducing one's desires....