After Dr. Ben Carson joked about falling asleep while waiting for a question during Thursday's Republican debate, viewers took to Twitter to deride the candidate's remark, saying his performance was slow and lacking energy. Once a top contender in the Republican presidential race, the retired neurosurgeon has been plunging in the polls ahead of February primary voting.

“I am very happy to get a question this early on," he said after receiving his first question of the night, adding "I was going to ask you to wake me up when the time came."

Critics have slammed Carson in recent months, saying he did not have enough political experience, particularly concerning foreign policy. Carson has been polling in fourth place among GOP candidates, with around 8 percent support, according to Real Clear Politics, which takes the average of the latest available polling data.

Carson is known in the media and online for his calm demeanor, and louder candidates such as Republican front-runner Donald Trump have often overshadowed the retired neurosurgeon. "You're going to see me not being quite so polite,” Carson told CNN ahead of the debate Thursday, promising to bring more enthusiasm than in previous debates.

Carson "actually looks asleep," tweeted comedian Moshe Kasher from his verified account. 

Journalists joked on Twitter about the candidate's performance.

Carson's campaign has lost some of its top advisers in the past two months alone, and his campaign finance chairman, Dean Parker, announced his resignation Thursday, just hours before the debate. Parker stepped down after an article in Politico alleged that he was paying himself a salary of $20,000 per month, which is unusually high for his position.

“While current allegations toward me are misrepresentations, my primary goal is to help Dr. Carson save our nation," said Parker in a statement, the New York Times reported. "I am excited about the growing momentum behind him and look forward to even greater days ahead,” he said.