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.”