HACKENSACK, N.J. — Marie Sullivan says that she knew something “wasn’t quite right” during a doctor visit, five years ago.

“I thought I might be anemic, but the results of my annual physical were fine,” the Paramus resident recalls. “All my numbers were in the normal range. The blood work turned up nothing. I said to my doctor, ‘Are you sure? What’s wrong with me?’ ”

Her doctor told Sullivan, “You’re getting older.” But Sullivan, 60, wasn’t buying it. “I’m not that old,” she says. “I used to have tons of energy. I know you slow down as you age, but I’m physically exhausted all the time. And I know I’m not the only person who feels this way.”

Lassitude. Weariness. Fatigue. Whichever phrase you prefer, recurring tiredness seems to be the new normal for a growing number of people, regardless of their age or background.

Causes range from illnesses such as anemia, depression, hypothyroidism, diabetes and heart disease to the increasing overuse of technology and its implications on our mental well-being.

Yes, Facebook, Twitter and Instagram can wear you out, says Dr. Patricia Bratt, a therapist and psychoanalyst with offices in Livingston and New York City.

“Social media can run the gamut from being fabulously uplifting to being totally depressing and exhausting,” says Bratt, who is also the director of trauma and resilience studies at the Livingston-based Academy of Clinical and Applied Psychoanalysis. “And this applies to all ages.”

Bratt works with young adults who check their social media constantly — at all hours of the day and night — and they all complain about being tired.

“It impacts their sense of themselves and their identities and makes them anxious,” she says. “Social media has created a new sense of impulsivity and urgency, it can make them feel overwhelmed by what is happening in the world, and all of these factors can be fatiguing and can impact how they sleep.”

Sleep apnea and poor diet are other common culprits of fatigue. And then there is the most obvious cause of all: not enough sleep, which often goes hand in with overwork.

In July, a survey conducted by the National Safety Council found that 97 percent of Americans have at least one of the leading risk factors for fatigue, which include working at night or in the early morning, working long shifts without breaks and working more than 50 hours per week. Forty-three percent of respondents said they do not get enough sleep to think clearly at work, make informed decisions and be productive.

Three years ago, Dominick “DJ” DeRobertis of Pearl River in Rockland County was one of those people. Now 39, DeRobertis works in the construction industry. He drives trucks, operates other heavy machinery and was having problems staying awake.

“I was sleeping two-three hours a night, waking up frequently and was always tired at work,” DeRobertis recalls. “I was taking these 15-minute power naps every two hours. It was bad. Then I put on some weight, and that just made it worse.”

Larry Rodriguez of Fort Lee had a similar complaint. A toll collector on the George Washington Bridge, he suffered from sleep apnea as well as shortness of breath, which he attributed, in part, to his work. “The hours, the fumes … I would wake up tired and I’d be tired all day,” Rodriguez says. “Then, I’d leave work and take a nap as soon as I got home.”

Both Rodriguez and DeRobertis took part in studies at the Sleep Center at Holy Name Medical Center in Teaneck and were diagnosed with sleep apnea.

Rodriguez now sleeps with a machine called a CPAP (continuous positive airway pressure), which delivers a steady stream of pressurized air into his airways. “And the results were immediate,” he says. “I still like a nap once in a while, but I’m not a zombie anymore.”

DeRobertis uses a variation on the CPAP called a BPAP (bilevel positive airway pressure) machine, which has an additional pressure setting. (The BPAP is used for patients who need to get more air in and out of their lungs while they sleep.)

“I can’t recommend it highly enough,” DeRobertis says of the BPAP. “It changed my life. I don’t have that constant tiredness anymore.”

STRESS, VITAMIN DEFICIENCIES AND OTHER CAUSES

While sleep apnea is relatively easy to diagnose, other forms of chronic fatigue are not.

Dr. Maria Vila, a physician at Atlantic Health System’s Chambers Center for Well Being in Morristown, says fatigue is one of the most common complaints among her patients. And, no, she doesn’t think “You’re getting older” is a particularly helpful diagnosis.

“I hear this all the time,” Vila says. “Patients are told, ‘You’re getting older … you’re a woman .. you’re menopausal … ’ and so on. That’s not what we do here. I start by looking at the patient’s history, their diet, exercise, sleep patterns and stress levels. Then I move on to blood tests. Almost everyone says they were told that their blood tests were ‘normal.’ But I’m not looking for normal. I’m looking for optimal.

“We look at the biochemical processes in your body,” Vila continues. “Is there a vitamin deficiency? We can test for that. Do you have elevated cortisol levels? Remember: Elevated cortisol can your affect your thyroid. What about food sensitivities? Dehydration? All of these things can cause fatigue and we address all of them, without medications. We use supplements, lifestyle changes, stress relief, massage, yoga … until those numbers come up. Again, we don’t want normal, we want optimal.”

STRESS SHOULD BE ADDRESSED

Gary Schulman, a certified fitness trainer from Oradell who works with clients coping with chronic diseases, including diabetes and arthritis, also favors a natural approach to fatigue and warns that people living with stress should not ignore it.

“People say stress can kill you, and they’re right,” Schulman says. “In today’s society, most people are on this disease continuum that I call stress without recovery. They’re dealing with stress from relationships, jobs, the toxins they put on their skin, the toxins they eat. And if they continue on that course, it eventually leads to chronic disease, thyroid problems, high blood pressure and more.”

Schulman says that every out-of-shape client who comes to him complains of recurring tiredness. His recovery plan: cardio workouts with some resistance training (beginning at a rate the client can handle), breathing exercises and stress management. As for diet, he urges clients to eliminate refined sugars and processed foods and limit or eliminate wheat products and refined carbs.

“Even if you’re not gluten-intolerant, it can cause inflammation and you’ll feel better without it,” Schulman says of the composite of proteins found in wheat. “As for sugar, the more you consume, the worse you’re going to feel and look.”

Dr. Vila isn’t quite as strict. “I don’t do everything right,” she says, “and I don’t expect people to do everything right. But diet-wise, if you can do 80 percent good and 20 percent bad, that’s a good place to start.”

(Keep in mind, though, that, even in moderation, sweets can wreak havoc with your body by causing your blood sugar level to spike and crash — a one-two punch that can trigger a dramatic and sudden loss of energy and feelings of lethargy and exhaustion.)

OTHER DISORDERS AND ENVIRONMENTAL FACTORS

Other causes of fatigue? Dr. Theophanis A. Pavlou, a pulmonologist focused on sleep medicine at the Sleep Center in Teaneck, deals regularly with sleep apnea patients. “But we also look for related disorders such as hyperthyroidism and hypersomnolence, which is a recurring desire to fall asleep,” he says.

For many years, extreme fatigue was linked to the Epstein-Barr virus, but Pavlou says, “We no long test for that, because everyone has had it. It’s so common that it’s not useful to know anymore.”

Pavlou urges anyone with sleep issues to take part in a sleep study. “People can have their doctor order one, as a prescription. Or they can see us first and expedite the process. It could be apnea, snoring concerns, insomnia, narcolepsy.”

It’s something many patients resist, Pavlou says, “because of the CPAP machine. Getting them to use one is the big roadblock. But it works, almost universally.”

And what about fatigued folks who don’t have sleep apnea, vitamin deficiencies or diet problems, but do have sleepless nights and a lack of energy during the day?

“We’re living in a very complex society,” says Dr. Carlos Rueda, chairman of behavioral health services at St. Joseph’s Healthcare System in Paterson, “and this causes all kinds of problems. We are dealing with perceived threats from everywhere, economic uncertainty, and we are in constant state of fight and flight. And, of course, people are constantly receiving stimuli from their computers and their phones. You need this if you want to stay competitive but this is also creating constant stress that disrupts sleep and disrupts your circadian rhythm.”

Dealing with these stresses, Rueda says, requires time management skills and re-learning how to relax. “Set a time, say 8 p.m. or 9 p.m., when you turn off your computer and TV screens,” he suggests. “We aren’t supposed to be receiving and processing information 24/7. Stop. Take a pause. You want to sleep better? Go sit under a tree and read a book.”