Imprisoned in a subterranean cell in an area of eastern Ukraine controlled by pro-Russia separatists for more than nine months, Anatoly Polyakov didn't know whether it was day or night and used hunger pangs to keep time for him.

“You have no idea what time it is, but you start to salivate when you sense they should bring food soon,” says Polyakov, who says he not only lost 40 kilograms during his captivity but nearly the ability to speak as he struggled to cling to his "humanity," as he describes it.

Polyakov, a successful businessman originally from the northern Russian city of Petrozavodsk, arrived in the separatist-controlled Donbas region of eastern Ukraine in the spring of 2015 on a humanitarian mission.

He helped transfer seriously ill children out of the conflict zone and negotiated a prisoner exchange before being snatched off the street and imprisoned by pro-Russian separatists in the Luhansk region.

Freed in 2016, Polyakov decided not to return to Russia and instead went to Kyiv to advocate for the rights of former Ukrainian prisoners of war (POWs).

He has helped craft draft legislation to ensure the returned Ukrainian POWs are guaranteed medical and psychological care as well as other benefits after they come home.

The bill, he says, has the backing of President Petro Poroshenko plus key members of the Ukrainian parliament, the Verkhovna Rada, and a vote is expected on it in the near future.

On December 27, the biggest prisoner swap since the conflict in eastern Ukraine erupted in 2014 took place, with 74 Ukrainian soldiers and civilians exchanged for 238 separatists.

“When the exchange took place, I was so happy. I called relatives, I had tears of joy. At the same time there were bitter tears as well, because I understood that our boys are still being held there,” recounts Polyakov.

By his count, 3,136 Ukrainians -- a near 50-50 mix of soldiers and civilians -- have been interned in what he calls the "death camps" of the so-called "people's republics" in parts of Donetsk and Luhansk that are controlled by pro-Russia separatists.

But he says only some 150 are still being held, mainly in Donetsk.

Polyakov's own ordeal began on March 15, 2015 after holding negotiations with separatist leaders in the city of Luhansk.

He was attacked on the street by masked men, quickly handcuffed and hooded before being bustled into a car. Torn clothing attests to the struggle he put up.

“Of my clothes, I was left with a ripped sweater and torn military pants. Nothing more,” Polyakov told RFE/RL's Russian Service in a recent interview.

Polyakov, who says he was targeted for his pro-Ukrainian views, ended up in a makeshift isolation cell somewhere in the Luhansk area.

“There was no daylight, no fresh air, and no way to maintain my personal hygiene. My skin took on a gray color, like the walls in the cell,” recounts Polyakov.

“I moved about the cell like a shadow, thin, with a full beard and long, shaggy hair. The fighters called me the ‘dungeon man.’"

Fresh air was a luxury in short supply in the cramped cell.

“There was a haze in the cell. It was unbearably hot, between 35-40 degrees Celsius. I would lay on the floor up against the door to get a bit of fresh air,” he says.

Barely fed, Polyakov fixated on food.

"At night you dream of food, and you’re ready to eat anything to kill the hunger," he explains. "It’s difficult to remain a human under such conditions.”

In January 2016, Polyakov was freed. While relieved, he still struggled.

“When I was freed from captivity I had all types of medical problems. I had lost 25 kilograms -- at the time I was freed I weighed 40 kilograms – and started making animal sounds like a dog barking,” explains Polyakov.

“Imagine all these animal sounds coming out of you and there’s nothing you can do to stop it. Believe me this was a very difficult period. I had to constantly cover my face and excuse myself when talking to someone, explaining that it wasn’t contagious."

Polyakov says he's been treated for the trauma he experienced, but stresses he is far from "cured."

“Today, two years after my release, I feel much better. The reasons for why I was making the animal sounds was explained. I’ve been treated, but I haven’t been cured. I still have to go to hospital for treatment every six months. I have to pay for everything,” he says.

Polyakov says his struggle to secure proper care spurred him on to advocate for the rights of returning Ukrainian prisoners of war (POWs).

“Of course, there should be long-term medical as well as psychological support for those freed, and not just one-time assistance," he says. "Physical and mental difficulties tend to arise in the third month [after release], sometimes after half a year, occasionally after a year. They fall into depression, experiencing a really difficult emotional time.”

Polyakov, who now heads the Ukrainian Association of War Prisoners, says he was swayed to stay in Ukraine after his experience.

"After captivity, all those who survived that hell have become my family,” he explains. “I consider myself a person with a Ukrainian heart and a Russian soul.”

Polyakov says the legislation would enshrine the right of former POWs to receive a wide array of services and rights, including protection from any “confessions” made while in captivity as well as a vow to bring to justice those who tortured them.

Polyakov says he's worked on the bill with other POW advocates for nearly two years, and he considers it therapeutic.

“I can’t say that I’ve fully adapted to civilian life. The only thing that gives me strength and energizes me is working on the POW status bill. That law is my rehabilitation.”

Read original story in Russian