Gramms has gone away. The retired high school chemistry teacher and grandmother is currently luxuriating under a bright beach umbrella, spending a well-earned vacation strolling along the soothing sand, nibbling at picnic fare and delighting in the cheery squawks of seagulls overhead.

Only here’s the thing: That balmy seaside spot exists only in her mind. Gramms, we come to find out, is battling Alzheimer’s disease, and is actually kicking up her feet in her own living room. Her flights of fantasy, and much are more, are revealed with spectacular nuance in Helium, the richly layered, unexpectedly upbeat play by Julian Wiles. The work is now refreshed from previous versions for Charleston Stage’s 40th anniversary.

With effervescent grace and quiet ingenuity, this poignant, yet never ponderous piece of theater triumphs in plumbing emotional depth, while casting warm light on the daunting terrain of aging and dementia. In Helium, the lines between the real and the imagined are as tenuous as the hold on a wind-blown balloon — and the play gently questions whether or not, at the end of the day, our standard-issue cognitive grasp is all that terribly important.

It’s true, the topic of Alzheimer’s — or any decline of a loved one — rarely elicits mirth and chuckles. More often, it is a subject that conjures despairing family members or disquieting events. However, in the capable, compassionate hands of Wiles and his fine cast, we are granted a rare vantage of both the disease’s serious challenges and its unfettered magnificence.

All this rests royally on the sure and poised shoulders of the show’s sublime leading lady, Samille Basler. As Gramms, the afflicted Southern senior, Basler blithely slips in and out of the sparkling, far-flung world in her head. Quick and willful, she cajoles us into her sand swept reveries, her intergalactic adventures and her visits to her former classroom days.

Using helium as its central metaphor, the play examines this noble gas and its majestic nature. Gramms, who regularly steals out of her home to purchase pumped-up balloons, is herself lifted above the ballast of the everyday. “You spend too much time living in the present,” she admonishes.

To remain aloft, she must navigate her anxious daughter Alice, who, as ably portrayed by Liz Duren, remains laser-focused on grounding her mother’s mental and physical roaming. To that end, Alice has enlisted the services of her two sons, the frustrated teenaged Ethan (in an on-point performance by Jacob Feight) and the younger, more agreeable Josh (the charming Parker Weeks). They thus add their own interpersonal pile-on to Gramms’ wanderings.

But Gramms isn’t alone in her imaginary travels. Ruth, her mild-mannered in-home caregiver is more than happy to go along for the ride, whether taking off with Captain Kirk and company in the USS Enterprise or doing a little globetrotting, a la Gramms. Ruth, who is played with tender resonance by Letty Clay, learns a great deal about life from her client’s daily excursions.

And it’s fun for us, too. While weighty in its exploration of one family’s grappling with dementia, it is wondrously light-hearted, powered by well-turned quips, funny bits and thought-provoking discourse that joins mind and matter in ways that are both insightful and healing. And, if you are like the audience of the performance I attended, then you may well hew to the old show adage: You’ll laugh. You’ll cry.

It’s cheery on the eyes, too. Wiles, who also served as scenic designer for the production, cannily set the work not in the living room where the action occurs, but on the beach. With merrily striped deck chairs and umbrella, a white wooden life guard box and a deep blue backdrop, the set enables us to better take the journey, too — and by doing so, to fully embrace the vibrancy that is part and parcel of Gramms’ displacement and confusion.

Moreover — and, heads up, I’m hereby placing foot firmly on soap box — it’s a subject that surely affects us all, but remains to my thinking far from sufficiently charted on stage and screen to broadly resonate. After all, whether you encounter dementia in a loved one or consider your own imminent dotage, the fraught and frightening prospect of Alzheimer’s inarguably bears deeper understanding. Works do exist, of course, like Florian Zeller’s gripping The Father, which enjoyed a run a couple of years ago by way of Village Repertory Theatre.

However, in Helium, we have homegrown work with a decidedly Southern, highly relatable protagonist. And it’s a work that has cracked the nut on a challenging issue often dodged, like the dispiriting mush Gramms must consume when she really prefers pizza and chocolate silver bells. In Helium, Wiles serves up the tough stuff of life in a way that both honors the topic — and delivers the pizza that is lively, laugh-laced theater.