Oh, Monday mournin’.

The first day of the workweek has long been maligned because it marks the startling shift from the weekend unwind to the weekday grind. It’s no coincidence that stress, heart attacks and even suicides have been shown to spike on Mondays, with the trend known as the “Monday effect.”

But then again, most US holidays are observed on Mondays — so maybe Mondays deserve a break.

In a new study, emergency physicians in South Korea make a case for Tuesdays as the real Workplace Wretch.

The researchers examined health data from over 200,000 adults to see how often cardiac arrests — when the heart suddenly stops beating — occurred on the first workday following a holiday break versus other weekdays.

They found that incidents of cardiac arrest were “significantly higher” — 9% to be precise — the day after a holiday than every other day of the workweek.

“This phenomenon was particularly pronounced among older adults, individuals with cardiac [history] and after two or more consecutive holidays,” the researchers wrote in JAMA Network Open.

So why this cardioverload?

Dr. Matt Pierce, director of the Cardiac Intensive Care Unit at Northwell Health’s North Shore University Hospital, has a few hypotheses to explain the potential link between a return to work and elevated heart risks.

“Theories include changes in sleep patterns and changes in your circadian rhythm going from a weekend back to a workweek, the stress associated with that,” said Pierce, who was not involved in the new study.

“Something else that’s theorized is that on weekends, especially holidays, people change their diet and alcohol consumption,” he added. “They consume more salt, and they consume more alcohol. And these factors also play a role.”

The idea is that the stress of staring down a new workweek triggers the adrenal glands to release heavy doses of the hormones adrenaline and cortisol, which rapidly spike blood pressure and heart rate.

Higher alcohol consumption also raises blood pressure and stiffens arteries, putting extra strain on the heart.

And finally, the shift in our 24-hour biological clock from weekend wine o’clock to clockin’ in for work boosts cortisol and makes the heart more vulnerable to damage.

To avoid the Sunday scaries, or the Monday scaries, depending on the holiday, Pierce recommends developing healthy sleep habits, like a consistent wake and bedtime; minimizing booze intake; and identifying ways to lower stress.

“Everybody needs to discover the stressors in their lives and things that can potentially calm them down and de-escalate the stressors,” Pierce said.

Weekday or weekend, there are “clearly connections” between stress, mental well-being and physical health, Pierce added.

“That was my biggest takeaway from this study,” he continued. “Whenever I see stuff like this or I’m reminded that connection exists, it makes me want to take a step back and make extra sure I’m taking care of myself and trying to be happy and stress-free as much as I can.”