“Thirty-one, and depression is a young man’s game,” lead vocalist Gareth David laments on the discordantly peppy track “5 Flucloxacillin” — one of the catchiest numbers from Los Campesinos!’ latest album, “Sick Scenes.” The song’s clinical title and frank discussion of self-medication may seem at odds with its sunny chords and infectious “whoo-oohs.” However, this juxtaposition sounds pitch-perfect coming from the notoriously quirky Cardiff-based seven-piece group. Another verse rattles off the line “hallowed be somnolence brought on by the Tramadol” as effortlessly as any late-2000s indie pop hook — and the fact that it somehow works is a testament to Los Campesinos!’ ability to wring ecstasy from the weirdest places. “Sick Scenes” — the band’s first full-length album in four years — gives a name to the kind of anxiety and search for purpose only vaguely alluded to on previous albums, like 2013’s “No Blues” and 2011’s “Hello Sadness.” It’s filled with the same tongue-in-cheek verbosity and rousing, ebullient arrangements that characterize Los Campesinos!’ past work. Yet, this time around, David and the band seem more self-aware as they figure out how to cope with growing older. This increased sense of perspective lends itself well to slower, more introspective tunes. One such track, “The Fall of Home,” blends gleaming piano and strings with surprisingly earnest lyrics. It wistfully describes the alienation felt upon returning home to a small town through disheartening sights such as an, “empty high street in pouring rain / funeral for a family pup / teenage pubs all boarded up.” Yet there’s also a sense of wonder underneath these expressions of melancholy. “A Litany / Heart Swells” characterizes intimacy as something both base and wholly uncontained. The song features distinctly unromantic declarations like “Now I feel the misery in your breast and mine / is one and the same and I feel close to fine.” These lyrics also mix the mundane with the magnificent, describing this moment, “Outside a chicken shop, a ceiling of stars / a nostril of Diet Coke, I'm back in your arms.” The song gradually builds momentum, swelling into the orchestral stirs and repeated mantra of a chorus suggesting devotion recurring on a cosmic scale — “I’m shouting out a litany, an echo calls back.” Likewise, the “heart swells” refrain is a wink-and-nod acknowledgment of continuity to love songs from Los Campesinos!’ earlier catalogue, namely “Heart Swells / 100-1” from 2010’s “Romance is Boring” and “Heart Swells / Pacific Daylight Time” from 2008’s “We Are Beautiful, We Are Doomed.” Most of the album’s other tracks showcase the band’s trademark sound in top form, featuring sickeningly upbeat melodies laced with razor-sharp reflections that count dysfunctional relationships, youthful belligerence and soccer among their common themes. Album opener “Renato Dall’Ara (2008)” is textbook Los Campesinos! — a feverish, feel-good thrill ride that skewers bourgeois oblivion with zingers like, “Pictured reading Karl Marx beside his parents’ pool, facing ridicule he bleated / ‘that doesn’t make me rich, no way, it’s only outdoor and it isn’t heated.’” However, the album never feels like it’s stagnating within its comfort zone. While the second track “Sad Suppers” is just as frenetic, its playful references like “don’t call it a come-on” and “behold the once and future me / sad suppers for the saudaddy,” also betray a creeping sense of ennui and angst. That doubt accelerates all the way up to the closing track, “Hung Empty” — a buzzing pop ditty remains incessantly hummable as it describes the narrator’s increasing sense of isolation. This sentiment is expressed in lyrics like, “I'm glad to be loved but I'm lonely / and I feel like I'm the only one.” The outro is sung just as brightly, even as it asks, “but what, if this is it now, what if this is how we die?” Los Campesinos! leaves that question unanswered, but at least they make existential dread something worth dancing about.