THE DANGERS OF “POST-HOSPITAL SYNDROME.”

But last September, Ms. Lewandowski entered a hospital after a compression fracture of her vertebra caused pain too intense to be managed at home. Over four days, she used nasal oxygen to help her breathe and received intravenous morphine for pain relief, later graduating to oxycodone tablets.

Even after her discharge, the stress and disruptions of hospitalization — interrupted sleep, weight loss, mild delirium, deconditioning caused by days in bed — left her disoriented and weakened, a vulnerable state some researchers call “post-hospital syndrome.”

They believe it underlies the stubbornly high rate of hospital readmissions among older patients. In 2016, about 18 percent of discharged Medicare beneficiaries returned to the hospital within 30 days, according to the federal Centers for Medicare and Medicaid Services.

Ms. Lewandowski, for example, was back within three weeks. She had developed a pulmonary embolism, a blood clot in her lungs, probably resulting from inactivity. The clot exacerbated her heart failure, causing fluid buildup in her lungs and increased swelling in her legs. She also suffered another compression fracture. . . .

Any hospital patient, or hovering family member, knows those stresses: Disrupted sleep, as staff draw blood and take vital signs at 4 a.m. A distorted sense of day and night. Unappetizing meals often served at inopportune times.

I haven’t been hospitalized since I was 3. But from staying with the Insta-Wife I’ve observed that the lack of sleep in particular is terrible, even when you’re not the sick one; a few nights spent in the hospital and I was a wreck every time. I once proposed an experiment in which we’d check perfectly healthy students into a hospital for a week or two, then evaluate their condition for change. I think we’d find drastic deterioration, and it might have trouble getting past the IRB because of risk. . . .