Short answers, pulled from the story.
Angst means an intense feeling of apprehension, anxiety, or inner turmoil. The word entered English in the 19th century from the Danish, Norwegian, Dutch, and German word angst, tracing back to the Proto-Indo-European root anghu-, meaning restraint.
Danish philosopher Søren Kierkegaard (1813-1855) is credited with first giving angst a specific philosophical meaning. In The Concept of Anxiety, he used the term to describe the anxiety humans feel when confronting the freedom and responsibility of unlimited choice.
Kierkegaard's angst referred mainly to ambiguous feelings about moral freedom within a religious personal belief system. Later existentialists such as Friedrich Nietzsche, Jean-Paul Sartre, and Martin Heidegger broadened the concept to include conflicts of personal principles, cultural norms, and existential despair.
Notable composers linked with existential angst include Gustav Mahler, Richard Strauss, Claude Debussy, Jean Sibelius, Arnold Schoenberg, Alban Berg, Francis Poulenc, Dmitri Shostakovich, Bela Bartok, and Krzysztof Penderecki. Their works emerged largely in the early 20th century alongside both philosophical developments and the experience of war.
Angst began to be discussed in relation to popular music in the mid- to late 1950s, amid concerns over international tensions and nuclear proliferation. Jeff Nuttall's 1968 book Bomb Culture traced angst in popular culture to Hiroshima, and the term became associated with folk rock, punk, grunge, nu metal, and emo.
The Latin angustia, meaning tensity or tightness, is a pre-cognate of the German Angst, sharing the same Proto-Indo-European root. The Ancient Greek word rendered roughly as ankhō, meaning to strangle, is also related, all carrying the physical metaphor of constriction.