BRUSSELS — Marieke Vervoort, the face of last year’s Paralympics and a marvel to millions through her stoic defiance of unremitting pain, accepts that her race is all but run.

Since those sunlit days in Rio, where she won a silver medal despite agonies so acute that she has signed euthanasia papers in her native Belgium, her illness, a form of progressive tetraplegia bewildering even to her doctors, has advanced with pitiless cruelty. To step into her fifth-floor bedroom here at Brussels’ University Hospital is to face the rarest sorrow of an athlete thinking only of when to die.

“I don’t want to suffer any more,” she says. “It’s too hard for me now. I get more and more depressed. I never had these feelings before. I cry a lot. Now even my eyesight is disappearing. An optician saw me and rated one eye two out of 10, and the other just one. He said there was nothing he could do, because the problem was coming from my brain. Then a neurologist stayed with me the whole night while I had one spasm after another. She said it wasn’t an epileptic seizure but just the body screaming, ‘I’m in so much pain. I’m done.’”

And yet through all the horror, there is a sense of grace in this scene.

Vervoort is not the type to solicit sympathy. She talks of her love of sparkling wine, she mockingly imitates Donald Trump’s thumbs-up gestures, and she laughs as her dog Zenn tries — and fails — to perform her party trick of balancing a morsel of food on her nose and then tossing it into her mouth. Plus, she has just published her autobiography, a diarized account of how a young woman betrayed by her body still won four Paralympic medals, not to mention acclaim as Belgium’s second-most influential sports figure, behind only Manchester City’s Kevin De Bruyne. She hopes that it will soon be translated from Flemish to English, because, as she puts it, she wants to use sport “to inspire as many people as possible.”

When she was younger and unburdened, she dreamt of being a sports teacher, even of pursuing elite track and field. But her exposure through the Paralympics has afforded her a powerful platform. She has received royal investiture from King Philippe, plus woman-of-the-year accolades alongside Angela Merkel. Sport has been both her reprieve and her release.

In this Sept. 10, 2016 file photo, Belgium’s Marieke Vervoort (right) and Canada’s Michelle Stilwell celebrate after the women’s 400m (T52) race at the Rio Paralympics. Yasuyoshi Chiba / AFP / Getty Images

Arranging an appointment with Vervoort is complicated, now that she has reached a stage when there are far more bad days than good. When I arrive, she is fast asleep after another bombardment of morphine. A few hours later, she calls, saying that she is ready to talk, and she does so lucidly, with an extraordinary mixture of passion and pragmatism. Every detail of her death, for example, has already been precisely choreographed.

She has written personalized letters to every person she cares about, stamped and addressed, to be read when the moment comes. She has suggested that her passing be marked by the opening of a red box, from which white butterflies are released. One thing is certain: the funeral will not be in a church. Not even the arrival of Christmas can persuade her to believe in any divine beneficence. As she has said: “If there is a God, it must be a bad guy to punish me this way.”

The Other Side of the Coin, her book is titled. To visit her in hospital, where she has been for two weeks for the removal of an infected portacath, a device in the veins often used for chemotherapy patients, is to see this terrible flip side in the flesh. Where the world has seen only the indomitably happy Paralympian with the lustrous smile, a couple of hours at her bedside reveals a suffering without end.

“So little sleep,” she sighs. “I can’t sleep at night. My psychologist knows it. I want her to be with me when I die. She works at the hospital, but even she says: ‘It is a lot that you are going through. I have never seen anything like this.’”

It is no exaggeration. Marieke is 38 years old and claims that she feels more like 90. Few people of 90, though, could countenance a deterioration like this. Once a supple and active teenager who enjoyed basketball, triathlon and deep-sea diving, she first noticed the warning signs when she developed repetitive infections in her Achilles, which grew so severe she had to walk on her toes. Soon afterwards, she could move only with the aid of the crutches. Then her legs stopped working altogether. Quite simply, she is being physically destroyed from the bottom up. Medics speculate that the paralysis is triggered by a deformation between the fifth and sixth cervical vertebrae, but are at a loss to explain the intolerable pain associated with it.

“I’m a Taurus,” Vervoort says. “If I want something, I go for it. I never give up easily. I didn’t want to accept that I would end up in a wheelchair. But in 2000 I couldn’t do it any longer, although I was still able to use my stomach and my back muscles. Even that has become less and less. Now I’m paralyzed all the way to my breasts. My finger function is going down as well. I have such a strong heart, but the pain medication is doing nothing any more. They have given me so many injections that everything is broken and hard. Sometimes the liquid goes in and comes straight back out.”

In this Sept. 5, 2012 file photo, Marieke Vervoort (right) beats Michelle Stilwell in the women’s 100m (T52) final at the London Paralympics. Michael Steele / Getty Images

Vervoort paints this picture to shed some light on the much-disputed ethics of assisted dying. Belgium has the most liberal euthanasia laws in the world, but they clearly mandate that three different doctors must agree that the patient is in a state of unbearable and incurable pain. Vervoort has long since passed this point. The paradox is that her agreement to end her life by lethal injection, in the hands of Dr. Wim Distelmans, has, in fact, helped extend it, by allowing her the freedom of choice to die peacefully and at the time she decides.

“They called him in the beginning ‘the murder doctor’ — but he saved my life. If he was not here I would have killed myself,” Vervoort says. “It is just so difficult to set a date. Whenever I do, they say, ‘Are you sure, Marieke? Are you really sure?’”

The date, inescapably, is approaching. While she rests, I speak to her father, Jos, a retired professor of tax law. “We are near,” he says. “She can’t eat properly any more. All she can cope with is pudding. Everything else she throws up. The end is coming.” He measures his words carefully, without any note of desperation. He just looks very, very tired.

Beside him is Zenn, the Labrador named to reflect Zen-like calm. She is nine, and besides cavorting in the corner with assorted treat and toys, she anticipates almost every grim twist of Marieke’s declining health.

“Everything I drop on the ground, she picks it up and gives it to me,” Vervoort says. “When I lose consciousness, she barks and the nurses come, and she stays licking my face until I come back around. She pulls out my socks, my jacket, opens and closes doors. She will stay with me forever. I could not even imagine giving her away.”

The people will cry, but I want them also to give thanks for the life I had, for the fact that I’m happy now I’m at peace

After a short operation, Vervoort will head back home to Diest, a little town about 65 kilometres east of Brussels, for Christmas. It will be the first since 2008 that she has not spent in Lanzarote, one of the Canary Islands, her haven of tranquillity away from the torment. “On New Year’s Eve, there is a custom of eating 12 grapes, one each second before midnight,” she says, excitedly.

“Then they release 1,000 balloons from a net. Now I’m too scared to go alone. But it’s my favourite place in the world. I want my ashes to be scattered in the ocean there.”

She hopes, too, that the unvarnished reality of her battle can be better understood. “Everybody sees me joyful, winning medals, being strong, but they don’t see the other side. That is why every Paralympian is, to me, a champion.” Even the silver that she grasped in Rio behind Canada’s Michelle Stilwell, in the T52 wheelchair racing class, arrived against a backdrop of trauma. “Nobody knows this, but three days before my first race in Brazil I was in hospital, because I was being sick constantly and dehydrating. I was so angry, and yet I came second. I suppose when you are mad, you are a lot tougher than normal.” It turned out to be her last appearance on the sporting stage.

There is no anger now, no energy for rancour at the degeneration of her faculties. Instead, there is only serene fatalism. She has withstood the ravages long beyond the customary limits of human endurance, even travelling to Japan with Zenn last spring to watch sumo wrestling and to see the cherry blossom. What preoccupies her now is the task of saying goodbye. Her parents, she says, will not be present when Dr. Distelmans sends her off to eternal sleep. “Too hard,” she says. “Very painful,” her father, agrees, quietly. “It is better that she does this with other people.”

But there will be champagne at the wake, and plenty of it. “The people will cry, but I want them also to give thanks for the life I had, for the fact that I’m happy now I’m at peace.” For the photographs, she needs one of her nurses to change her top from the standard-issue hospital smock. While I wait in the corridor outside, more injections are administered, and her screams are curdling.

Walking back in, I find her face again a diagram of anguish as another sleepless night awaits. The clock has struck 8 p.m. and visiting hours are over. She stretches forward and places a hand in mine. “The best goal you can have,” she says, “is to make people happy.” She can count it as a goal fulfilled.