“Mad Men,” Matthew Weiner’s beautiful but often frustratingly occluded portrait of the American 1960s (as experienced by a group of people who work in advertising), has entered a permanent dream state.

The show’s seventh season begins Sunday on AMC in the same hazy, anxious, uncertain manner that encumbered its previous season. It’s hard to tell if what we’re seeing is meant to be taken in any way as a linear story; more and more, it unfolds like a hallucination — David Lynch minus the dancing dwarf — or a vivid drug trip that’s appropriate to the era. Maybe this is how “Mad Men” is supposed to end, with less clarity and order than it started out with, as one giant analogy to the decade it portrays. Someone’s having this dream, but you’re not sure who it is.

As viewers probably know, “Mad Men’s” final season has been cleaved in two — seven episodes starting now, with the final seven episodes scheduled for 2015. When a show has this much creative control over its ending, the best metaphor is that of an airplane’s final approach, circling long and low for a landing.

Fittingly, “Mad Men” is promoting itself with the visual language of air travel — posing its cast in customary high style against the long-gone glam of late-’60s airport terminals and enviably roomy commercial flights.

Underlying this mood is the state of things in the company formed last season in the merger of New York-based ad agencies Sterling Cooper Draper Pryce and Cutler Gleason Chaough. A big Sunkist account opened up a world of California dreamin’ for the “Mad Men” gang, causing most of the executives, including Don Draper (Jon Hamm), to covet the chance to head up a new Los Angeles office.

Don instead fell into a shame spiral that rivaled all his previous gloom after his teenage daughter, Sally (Kiernan Shipka), caught him in flagrante delicto with Sylvia Rosen, the cardiologist’s wife. At the end of last season, Don came apart during a presentation for a Hershey’s chocolate campaign and told everyone present that he was an orphan who was raised in a whorehouse, which viewers, who’ve seen the flashbacks, accept as true (with good reason). The partners asked Don to take an unspecified leave of absence; the L.A. move was out, but Don’s wife, Megan (Jessica Paré), went west anyhow, in search of TV stardom.

When Weiner sends an advance copy of the season’s first episode to critics (and there is only ever the one episode), it comes with his plea to keep every last detail under wraps: Is Don still employed? What month and year is it on the calendar? How did Sally react to that road trip at the end of last season, when Don showed her where he was raised? Is Don embarking on a new life as an honest man? Or is this just another iteration of midlife crisis?

It’s easier this time to obey Weiner’s request because there’s so little left that’s worth a spoiler alert. The ’60s are ending, and California is clearly where it’s at — and perhaps where this story intends to die.

Sunday’s episode features a gorgeous slow-motion sequence of Don getting off a plane and moving through the vibrantly tiled hallways of LAX and out to the white zone, where Megan, in the shortest possible wisp of a dress, waits for him next to her convertible. Everything is bathed in diffuse Angeleno light. Not a micron is out of place; for people who only ever watched the show for this sort of detail, it’s a divine vision.

“The New Yorkers here, they brought as much as we need,” a tanned, freshly single and spaced-out Pete Campbell (Vincent Kartheiser) effuses over a pastrami sandwich in an L.A. deli.

There is a corresponding feeling in this episode that New York is a hollowed shell of itself. Back at the office, there is a sense of decay. Joan Harris (Christina Hendricks) and Roger Sterling (John Slattery) seem to be separately suffering from whatever malaise affects characters who’ve ceased to be interesting. Peggy Olson (Elisabeth Moss), who some of us still consider to be “Mad Men’s” central protagonist, struggles against the creative void left in the wake of Don’s meltdown.

Airplanes, red-eye flights, terminals, arrivals, departures. (Crashing? Missed connections? Hijackings?) A viewer who overthinks it all will surely want some message in the flight moitf, which is all probably just one more “Mad Men” tease.

However, having recently read journalist Brendan I. Koerner’s excellent history of America’s bizarre hijacking epidemic circa 1970 (called “The Skies Belong to Us”), I’d love for the melodrama-adverse “Mad Men” to experiment with a brief jolt of action and send one of its characters on an unhappy, unscheduled flight to Algeria.

This is no more ridiculous a suggestion than the one from a certain strain of “Mad Men” fans who still harbor the dark hope that Megan is headed for a house party that will be rudely interrupted by the Manson family. “Mad Men” viewers are prone to such misplaced desires because “Mad Men’s” empty spaces give us such long layovers in which to mull and brood.

Weiner and company have 14 episodes left to tell us what this journey really amounts to, but all along it’s been about the exchange of one kind of American culture (male, white, moneyed, chain-smoking) for another, broader, chaotically diverse society that will come along after “Mad Men’s” time.

Even though the show has subtly indicted the old-fashioned, discriminatory attitudes of the mid-century — particularly where gender is involved, less so with concerns to race — one can’t help but also admire “Mad Men” as a sad elegy for a lost sense of order. The show is sentimental about people dressing up to go to work and attend social settings and catch flights at airports; it celebrates strong design, clean lines, a sense of what some might still call proper. In its early seasons, “Mad Men” exulted in these features of the ’60s and then sullied them with adultery, cruelty, deception, depression.

Now “Mad Men” leans toward a hint of the 1970s, where all things go to seed. The show seemed uncharacteristically clumsy last season in its depiction of 1968, verging on a paisley-and-hippy themed costume party as it tried to get the details as perfect as it had in earlier seasons.

Here, in January 1969, the show has located that groove; it simply looks more confident and real again. Its characters are starting to adopt the casualness of the era. The freer they get, the more they let their hair down (literally or so to speak), the unhappier life seems. Surely this can’t only be a subliminal vibe occasioned by the costume department; “Mad Men” and its viewers find the encroaching ’70s repellent.

This is a commonly held aesthetic opinion about American culture: The ’60s were beautiful, and then the beauty was destroyed, in part by the mainstreaming of counter-culture. It’s an “Oz” effect, in which America goes from black-and-white to a vivid anarchy that prefers the sloppy, the poly-blend, the scantily unkempt. The ’70s will arrive just as the show winds down; the colors run together and become garish, leaving us in that Watergate-era beige brutalism that we’ve learned to love only ironically.

Does anyone ever page through a family photo album and remark at how much more beautiful everyone looks in the ’70s than they did in the ’60s? (Usually it’s the other way around — the ’60s photographs are rescued and scanned and shared on Facebook and funeral videos; the ’70s photos are mocked on Throwback Thursday.) This isn’t only about clothes; it’s a commentary about people: What happened to us? Where did it go wrong?

“Mad Men’s” trip from the dapper to the drab is very much like a contemplative stroll through the National Gallery of Art’s current exhibit of the fleetly observant and prolific work of the photographer Garry Winogrand, who shot pictures of everyday New Yorkers in public from the early 1950s to the late-’60s: It’s businessmen in elevators, fancy ladies en route to appointments and the basic spectacle of pedestrian life.

Winogrand also adored what went on in airports — the possible narratives in coming and going; arrivals and departures; welcoming and parting. Viewed alongside the new “Mad Men” publicity stills that fetishize the ’60s travel experience, one is reminded that the TV show is only a TV show, an idea of reality heaped with pure fantasy.

Like the advance team from Sterling Cooper, et al., Winogrand relocated to Los Angeles, right when the seedy ’70s kicked in. In those later photographs, LAX is a decidedly less glamourous destination, dressed-down and overpopulated with sun-blasted refugees from the America seen in his earlier, New York-centric photographs.

Progressing chronologically through Winogrand’s pictures, it’s not hard to imagine Don, Roger, Pete and everyone else suffering the indignity of the disco era. The National Gallery show (which runs through June 8) is the perfect complement to a “Mad Men” binge, especially as the subject matter extends several years beyond where the show will probably end.

Perhaps “Mad Men” is crashing and burning before our eyes. It’s as watchable as ever, and also as unsatisfying as ever, as it veers toward the helter-skelter. What is its strongest theme? What question is it trying to answer? Who is the most important character here? Watching Sunday’s episode further broadens the field of possible (and wacko) answers, up to and including a sneaking suspicion that there is no such thing as Don Draper — even beyond his stolen identity.

Wouldn’t that be something, for Weiner to reveal that Don was just a figment, a ghost? If any show has the right (or the courage) to pull the lever marked “it was all just a dream,” shouldn’t it be “Mad Men?” Because in every way that matters, it already is a dream.

Mad Men

(one hour) returns Sunday at 10 p.m. on AMC.