They were in zero G for 8 months, that takes a toll on the body.

Astronauts are regularly hospitalized after extended stays in space. Here’s a guy who was up 12 months:

https://abcnews.go.com/Health/1-year-space-body-nasa-astronaut-frank-rubio/story?id=103406478

“During this period, there is a decrease of muscle mass – due to decreased use and lack of stimulus through exercise equipment – and bone loss.”

“She said one of the areas that she sees crew members struggle with upon returning to Earth is neurovestibular challenges, or how the body maintains a sense of position and balance, as gravity changes.”

"The longer the mission, the longer it can take to acclimate, Fogarty said. Four- to six-month missions make take two to three days. Longer missions would likely take even longer.

Additionally, because of the weightlessness in microgravity, blood and cerebrospinal fluid often shift upward from the lower extremities to the head and eyes, which is believed to cause eye and brain structural changes.

This is a phenomenon known as Spaceflight Associated Neuro-ocular Syndrome and long-duration astronauts may experience a variety of changes including an upward shift of the brain or eye swelling and blurry vision."

I remember an interview when Scott Kelly returned and he described the intense pain he was dealing with post splashdown. Specifically the massive amount of swelling in his feet and legs.