Right after revealing that he is HIV-positive, Charlie Sheen penned an open letter on the "Today" show's website, in which he opened up about his diagnosis and detailed how dealing with his sickness sent him into a "suicide run."

"Roughly four years ago, I suddenly found myself in the throws of a seismic and debilitating three-day cluster-migraine-like headache. I was emergently hospitalized with what I believed to be a brain tumor or perhaps some unknown pathology," wrote the 50-year-old. "I was partially correct. Following a battery of endless tests, that included a hideous spinal tap, it was sadly and shockingly revealed to me that I was, in fact, positive for HIV."

The actor compared the news to "a mule kick" to his soul. Sheen said the words were impossible to absorb, admitting that he tried to convince himself that he was "stuck, suspended, or even stranded inside some kind of alternate reality or nightmare." However, Sheen realized he was awake and his diagnosis was "true."

The actor sought care from leading infectious diseases specialist Dr. Robert Huizenga and began what he called "a rigorous and intensive treatment program."

"Not missing a beat, a med dose, or one shred of guidance, quickly my viral loads became undetectable. Like every other challenge in my life, again, I was victorious and kicking this disease's ass," wrote Sheen. "I wish my story had ended there. Unfortunately, for my family and myself, it had only just begun."

The actor said his diagnosis led him into a downward spiral where he began abusing drugs and alcohol. His substance abuse later led to Sheen's behavioral issues, including his very publicized 2011 meltdown that got him fired from his role as Charlie Harper on CBS' "Two and a Half Men," which he had been portraying since 2003.

"The personal disbelief, karmic confusion, shame and anger lead to a temporary yet abysmal descent into profound substance abuse and fathomless drinking. It was a suicide run. Problem was, I'd forgotten that I'm too tough for such a cowardly departure. Yet, despite this loathsome and horrific odyssey, I was vigilant with my anti-viral program," he wrote.

"My medical team could only shake their heads as each and every blood test returned levels revealing a state of remission. Even though I might have been trying to kill myself, one thing was radically evident; the disease was not."

The Golden Globe winner admitted to seeking the company of "unsavory and insipid types" and, despite his relationship with those of "salt-like reputation," Sheen said he was always honest about his condition and used condoms. But, the father of five revealed that some women used his secret against him. His personal truth "became their treason, as a deluge of blackmail and extortion took center stage in this circus of deceit."

"To date, I have paid out countless millions to these desperate charlatans," he said about those who extorted him. "Locked in a vacuum of fear, I chose to allow their threats and skulduggery to vastly deplete future assets from my children, while my 'secret' sat entombed in their hives of folly (or so I thought)."

For Sheen, revealing the truth put an end to all the secrecy. The actor has reevaluated his life and has made positive changes — starting with proclaiming that his "partying days are behind him."

"I'm claiming back my freedom," he stated. "The scales of justice will swiftly and righteously re-balance themselves. In conclusion, I accept this condition not as a curse or scourge, but rather as an opportunity and a challenge. An opportunity to help others. A challenge to better myself.

"Every day, of every month, of every year, countless individuals go to work, man their stations, fulfill their professional obligations with a host of disabilities. Diseases, imperfections, hurdles, detours. These maladies range from lupus to cancer, from paralysis to blindness, from diabetes to obesity. 'Treated,' HIV is no different. My partying days are behind me. My philanthropic days are ahead of me.

"Ernest Hemingway once wrote, 'Courage is grace under pressure.' I've served my time under pressure; I now embrace the courage, and the grace. Love and peace, Charlie Sheen."