March 7, 2013  -- A man who was driving across country in 2005 and found himself thrown in a New Mexico jail for DWI, and then spent nearly two years in solitary confinement, has won $15.5 million in one of the largest prisoner civil rights awards in U.S. history.

Stephen Slevin, 59, was depressed in 2005 when he decided to drive across the country, with no particular goal or destination in mind, his lawyer Matt Coyte told ABCNews.com. After being pulled over in Dona Ana County, N.M., on Aug. 24 2005, Slevin was arrested on aggravated DWI charges, and for driving a vehicle that he did not own. He was brought into the Dona Ana County Detention Center.

From there, his long nightmare began.

"To find out what happened was difficult," Coyte said. "His mental health was so compromised from his time in jail, he had very little memory of his stay there."

By piecing together documents and records available from the lockup, Coyte said he discovered that after his arrest, Slevin was soon placed in padded cell in the jail's floor, naked with only a suicide smock on, as what Coyte believes was a form of detoxification.

The cell was like a "horrific version of a drunk tank," Coyte said.

Slevin then went into medical observation for a few weeks. He was placed in an observation cell with its own shower, toilet and a window so he could be observed. From there they transferred him to solitary confinement, where he would spend the next 22 months.

Dona Ana County's policy, Coyte said, is to put all prisoners deemed mentally ill into solitary confinement. Jess Williams, the Doña Ana County director of public information, said that's just not true.

"That's not correct, that's never been the policy," he told ABCNews.com "He was placed in administrative segregation at his request. He did not want to be in the general population."

Doña Ana County released a statement in January stating that Slevin was offered an opportunity to join the general population in a cell block with a day room, but refused, and the only option was to place him in one of the facility's 28 administrative segregation cells.

Over the first three months in the segregation cell, Slevin was able to write letters, some of which were to his sister, others of which were what Coyte called very polite correspondences asking his jailers for assistance -- stating that he needed medical attention, that he couldn't sleep, or he was starting to have panic attacks.

In January 2006, after three months in solitary confinement, Slevin became delirious.

"He was incapable of writing at that point … You can see he was shaking in his writing. What he needs is to get out of that cell," Coyte said.

At that point he sat back and forth and began rocking. From January 2006 until May of 2007, "he just rocked back and forth," Coyte said.

Slevin would only get out of his small cell at first, a few times every month. After that, there were periods up to four months when he did not leave. Though he was given food and medication during these periods, he was not bathing. He had fungus on his skin, Coyte said. And his teeth were rotting.

When his prisoner rights case went to trial, Coyte said that the defense claimed that Slevin had wanted to be in solitary, and that he had the ability to get out whenever he wanted. That was contradicted by guards who testified at the trial, he said.

While he was being held, Slevin's DWI case was stalled after a lawyer raised the issue of competency. The case was delayed, Coyte said, as medical evaluations were meant to take place.

"In this county, if a person is dangerous, they want to hold him. That's the political culture of that county," he said. "Many counties do this."

Williams told ABCNews.com that if Slevin had requested it, he would have been evaluated. He said he wasn't aware if Williams had requested an evaluation.

On May 8, 2007, Slevin was released from solitary and sent to the New Mexico Behavioral Health Institute n Las Vegas, N.M. Once there, he was slowly re-socialized with other people, and was given medication. Coyte said that it was only a matter of days before he was returning to normal.

"He was thinking, 'where have I been?' Coyte said. "He thought it was a matter of months. He was shocked to find out he's been gone for so long. They had him figured out quickly. If you treat him like a human being, he becomes one."

But after two weeks, Slevin was sent back to Dona Ana County jail, and was returned to the same solitary cell. He began to deteriorate again. In this period he had an abscess on a tooth. Without any medical attention he twisted it back and forth for eight hours until he was able to rip it out, his lawyer said.

On June 22, 2007 the charges against Slevin were dismissed by a district court judge. Coyte said that he believes a judge who saw his case must have had pity on him. Three days later he was released, and was picked up by his sister, who having stopped receiving letters, had thought she had somehow angered her brother.

Coyte said that no one would take Slevin's case. In the legal community, he said, there is a belief that no one will value the pain and suffering of someone who was in jail. But he decided to take the county on.

The case went to trial in January of last year. During the trial, Coyte brought into the courtroom a replica of the pod-like cell that Slevin was kept in for jurors to see.

"We were able to prove they were indifferent to the conditions of confinement that Slevin was subjected to," Coyte said.

Testimony during the week-long trial from guards who had worked at the Dona Ana County Detention Center painted a picture of Slevin being kept in the conditions he described, and overall poor management of prisoners, Coyte said.

Slevin was awarded $22 million by a jury. That amount was appealed, and on Feb. 12 they settled for $15.5 million, which was announced this week.

The Doña Ana County Board of Commissioners released a statement Tuesday saying that it "deeply regrets the harm Mr. Slevin suffered during this period [of incarceration]."

The release also points out that since 2006 the detention center budget has nearly been doubled, which has been "channeled toward improved staffing, training and inmate access to care and services."

Williams, the county spokesman, told ABCNews.com that the length of time Slevin was held was out of the jail's hands.

"One of the things people are focusing on is length of time he was in. We have no control of that," he said. "The district attorney, the court, the public defenders determine the pace at which the case was resolved. Our responsibility is holding him. The schedule of prosecution is out of our control."

Now a free man, Slevin is fighting lung cancer. During the trial, it came to light that his doctor gave him a year to live -- a fact that didn't deter him from fighting his case until the end.

Coyte would not say where Slevin is living, for reasons of privacy. He said that he suffers symptoms of extreme post traumatic stress as a result of the "torture" he endured.

"He's never going to get it back," Coyte said. "Hopefully he'll beat the cancer. But you never know. Right now, hopefully the money will help him to do better."