It’s depression.

Two years ago, Canada’s Rebecca Marino, then 20, was rising in the world of tennis. This despite the fact that every time she played, Marino faced another opponent besides the one across the net.

Depression, writes Andrew Solomon in The Noonday Demon, “is the aloneness within us made manifest, and it destroys not only connection to others but also the ability to be peacefully alone with oneself. … In depression, the meaningless of every enterprise and every emotion, the meaningless of life itself, becomes self-evident.”

As a result, Solomon, a fellow sufferer, writes, “depressed people can barely manage to get out of bed and put on their shoes and socks.”

Marino suffered from the illness for years, yet managed to become the 38th-ranked player in the world. In 2011, she had a setback, triggered in part by cyberbullying — many of the nasty messages coming from people who had lost money betting on Marino’s matches.

“I don’t want to discredit social media,” Marino said, “but personally I find it quite distracting. Getting some comments on there that were very hurtful. The hurtful ones stick to you. I was getting messages that I should go die or I should burn in hell, and that was just scratching the surface.”

People with depression — that’s 1 in 10 Americans, according to the National Institutes of Health — are particularly susceptible to bullying, and though Marino eventually ended her Twitter and Facebook accounts, the damage had been done.

Last February, she walked away from the game. She returned seven months later to give it another go. On Wednesday, she put her racquet down again, saying, “I do not think it is worth sacrificing my happiness for.”

Along with battling depression, Marino had also faced the stigma that often attends it.

As Joyce Carol Oates wrote in a 2001 review of Solomon’s book, “Our common-sense culture can generously accommodate physically ill individuals, but the mentally ill can be suspected of exaggerating, even of imagining, their own problems. Their minds, or brains, must have ‘caused’ their ailments, since we have only the testimony of the afflicted to bear witness to what is ‘ill’ in their lives.”

Marino told reporters on Wednesday, “I am opening up to you all about this because I would like to get rid of the stigma attached not only to depression but also to mental illnesses both in the public and in professional sports. If I can share my story and change one person’s outlook or life, I have reached my goal.

“Depression is nothing to be ashamed of.”

Unlike cyberbullying.

“You hear about bullying, it exists on all levels,” Leafs defenseman John-Michael Liles told The Toronto Star. “It’s not just high school. It’s towards athletes, co-workers, whatever,” he said. “It’s tough because I think when you have a computer or have a cellphone, there’s a lot of anonymity.”

Anonymity, in this case, equals cowardice. The opposite of cowardice is Marino’s decision to bare her problems to the world.

“Don’t be afraid of the stigma of it, and talk about it,” she told The New York Times. “There’s nothing to be ashamed of. If you’re being bullied, or cyberbullied, or someone’s harassing you, it’s better to be open about it and talk to someone about it than to hold it inside.”

Contact Jim Gordon at gjames43@msn.com.