How do you feel on Sunday evenings? Is there a knot in your gut? Do you keep an anxious eye on the time and wish it would stop reminding you that, come tomorrow, it’s no longer your own?

A case of the Mondays is a real thing. And our bodies keep the receipts.

A new study from the University of Hong Kong shows that Mondays, in their own unique, awful way, drive long-term biological stress. For some of us, this holds true even if we’re no longer part of the rat race.

The study analyzed data from more than 3,500 older adults 50 and older who took part in the English Longitudinal Study of Aging between 2012 and 2013.

They found that the adults who reported Monday anxiety had 23% higher cortisol and cortisone levels in their hair samples, compared with those who regarded Mondays as just an average day.

Some participants who reported high stress weren’t working, suggesting that job stress isn’t the only explanation for the heightened anxiety.

Scientists already knew that Mondays are linked to a 19% spike in heart attacks. The new study identifies what is known as the hypothalamic [high-po-tha-lam-ick]-pituitary-adrenal axis — they call it the HPA for short — as a possible biological reason for that spike.

When the hormone cortisol is chronically high in our bodies, it contributes to high blood pressure, insulin resistance and immune dysfunction. All of these can drive heart disease.

So, how do Monday fretters find peace? Try reserving Sundays for self-care. Give yourself a facial. Or go on a hike. Turns out, a dedicated moment for taking care of yourself may be one of the few social media trends actually backed by science.