I’ve been disabled since I was 24 and have experienced recurring bouts of major depression for most of my life.

And like a crow with a carcass, one tends to feed off the other.

Because of my impaired mobility — most days I’m confined to bed for 22 hours — it’s often impossible to exercise enough so that my brain releases sufficient endorphins, one of the hormones key to experiencing joy.

And what’s one of the first treatments that physicians and mental-health professionals recommended for depression? Exercise.

Without that tool in my arsenal, it sometimes feels as if I’m fighting a war on two fronts, equipped with only a butter knife and Silly String.

So, what do you do when one of the most effective and least expensive treatments is no longer an option? It’d be great if more clinicians addressed this question and understood that many disabled people cannot exercise to the degree that we’d like or, indeed, at all. And that this dynamic only intensifies our depression.

Disability is a huge tent and those of us within it don’t face identical obstacles — I have myalgic encephalomyelitis, also known as chronic fatigue syndrome. But according to the Census Bureau, 1 in 5 Americans has some form of disability. And mobility is a struggle for many of us. Millions of people are too often overlooked while we combat a pernicious mood disorder.

For me, the warning sign is when I start editing and reediting the playlist for my funeral. That’s how I know the depression is back.

After calmly and methodically debating whether I want my eventual send-off to open or close with the Rolling Stones’ “Before They Make Me Run,” the still-cogent part of my mind hears this grim, existential party planning and thinks, “Uh-oh.”

If you’re disabled and depressed, it’s important to figure out your own substitutes — or in some cases, addendums — for exercise. I reach out to a loved one and ask if it’s convenient to talk for a bit. I call my therapist and make an appointment to troubleshoot.

Meanwhile, I curl up with my Pomeranian, Thomas, who loves to spoon and thinks all my time should be devoted to him anyway. Using my walker (I’ll get to that in a sec), we stroll and I watch him watch birds — it’s like a Disney cartoon come to life — and for the time being, my heart stops feeling as if it might detonate. Once more, I opt to stay tethered to Earth.

Because despite my sometimes uncooperative neurochemistry, the larger part of me really does want to live. So I’ve got to remain vigilant. And while it’s easy to make jokes about the Stones and to get all Dr. Doolittle with the dog, the reality, of course, is that depression can kill.

And mine has been trying to do so since I was 12, when I experienced suicidal ideation for the first time. It runs in my family: several forebears grappled with depression, too, and at least two tried to kill themselves decades ago.

I’m grateful that I benefit from the scientific, therapeutic and social advances that have occurred since then. The antidepressant Celexa works for me and blunts the sharpest edges, as such. My therapist allows me to pay a sliding-scale fee. And I’ve long been open about all of this with my family and friends. I don’t ascribe stigma to it and neither do they.

I’m also grateful that I can still walk at all. I know far too many who cannot, who’d gladly walk as well as I do on my worst days.

And I’m extremely fortunate that I can work from bed. Indeed, with the exception of my first two plays, everything that I’ve published — including my first book and the second one that I’m completing now — has been written from bed. Or, as I refer to the sprawling mound of books and notes obscuring my floral duvet cover, “Mission Control.”

Regardless of one’s physical ability, perhaps depression’s greatest paradox is that it requires massive discipline exactly as your mind is trying to convince you — in a voice that sounds eminently reasonable — that life is meaningless and that, for good measure, you should watch “The Office” in totality for your 15th time.

Exercise is extremely effective at silencing that voice. Which is why I still walk a mile to a mile and a half most days. I must use the walker, proceed slowly, and stop frequently. It keeps me toned and I love getting out of the house. But as my internist corroborated, at that pace, my brain is producing few endorphins, basically tossing me its spare change instead of paying the bill.

The late Broadway legend Elaine Stritch used to quote her husband, “Everybody’s got a rock,” an eloquent way to sum up the struggles each of us faces. These just happen to be mine.

But until science more effectively incorporates the millions of us with physical disabilities and mood disorders, those rocks will continue to feel like boulders that might crush us.