Short answers, pulled from the story.
Psychedelic music is a wide range of popular music styles influenced by 1960s psychedelia and the use of drugs such as LSD, mescaline, DMT, and psilocybin mushrooms. Its defining features include Eastern instrumentation like sitar and tabla, disjunctive song structures, modal melodies, extended improvisation, backwards tapes, electronic phasing, and keyboard instruments such as the Mellotron.
Psychedelic music emerged during the 1960s among folk and rock bands in the United States and the United Kingdom. Sandy Bull's 1963 album Fantasias for Guitar and Banjo is considered one of the first psychedelic records, and the 13th Floor Elevators coined the term psychedelic rock in January 1966, releasing The Psychedelic Sounds of the 13th Floor Elevators in October of that year.
Several factors drove the decline. LSD was declared illegal in both the United States and the United Kingdom in 1966. The Manson Family murders, linked in the press to Beatles songs including Helter Skelter, fueled an anti-hippie backlash. The fatal stabbing of Meredith Hunter at the Altamont Free Concert on the 6th of December 1969 further undermined the movement's optimism.
Psychedelic rock served as a bridge between blues-oriented rock and heavy metal through its distorted guitars, extended solos, and adventurous compositions. Jeff Beck and Jimmy Page, both former Yardbirds guitarists, went on to form The Jeff Beck Group and Led Zeppelin. Black Sabbath, Deep Purple, Judas Priest, and UFO also began as blues-based psychedelic bands. King Crimson's 1969 album In the Court of the Crimson King is seen as a link between psychedelia and progressive rock.
Acid house originated in Chicago in the mid-1980s with DJs including DJ Pierre and Phuture, whose 1987 track Acid Tracks coined the genre name. It built the squelchy, bass-heavy sound of psychedelia into house music using the Roland TB-303 synthesizer. By 1988's Second Summer of Love it had become a mainstream phenomenon in the United Kingdom.
Chillwave is a synth-based style of psychedelic music coined by blogger Carles on the Hipster Runoff blog in July 2009. It is characterized by mellow beats, vintage synthesizers, and lo-fi melodies, and overlaps with related terms including glo-fi and hypnagogic pop. A 2009 Pitchfork review described the shared sound as psychedelic music that is synth-based, 1980s-referencing, cassette-oriented, and hazy.