Has the bitcoin fever broken?

Bitcoin prices plunged sharply to below $11,000 on Friday, shedding a third of its value in just 24 hours, according to data from CoinDesk.com. It later rebounded slightly to around $12,000 -- but that's still a stunning 25% less valuable than bitcoin was Thursday morning.

Prices had approached $20,000 as recently as Sunday.

The price drop comes on the back of a few days of bad news for bitcoin, which has still soared by more than 1,000% since the start of the year.

On Thursday, a bitcoin spinoff called bitcoin cash was suspended from one of the most popular exchanges after possible insider trading.

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Meanwhile, the U.S.'s markets regulator halted trading in a red-hot bitcoin stock.

Earlier in the week, a South Korea-based virtual currency exchange was forced to close its doors after falling victim to two attacks by hackers in the space of a few months.

The incidents have raised questions about the reliability of cryptocurrency markets, which aren't regulated by governments or central banks.

But some argue bitcoin is just taking a breather -- albeit a big one -- after a furious 2017.

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"A correction like we are witnessing today is hardly surprising," said Dave Chapman, managing director of Hong Kong cryptocurrency trading platform Octagon Strategy.

Amid the turbulence Friday, one of the most popular cryptocurrency exchanges, Coinbase, said buys and sells might be "temporarily offline" due to high traffic.

The plunge threatens to take the shine off what's been an incredible year for bitcoin. This time last year the virtual currency was worth less than $1,000.

The rally has been driven partly by the expectation that more and more mainstream investors will begin trading it.

Earlier in December, two major U.S. financial exchanges launched trading in bitcoin futures, which will help give it more clout with big, institutional investors.

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Bitcoin's dizzying ascent has prompted a number of high-profile figures in finance and economics to sound the alarm, cautioning that the currency's boom is simply a huge bubble.

Among them are outgoing Federal Reserve Chairwoman Janet Yellen, who described virtual currencies as "highly speculative."

However, Shane Chanel, an adviser at Australian investment firm ASR Wealth Advisers, thinks investors could start shifting their focus to virtual currencies other than bitcoin over the coming months.

"I feel the cryptocurrency madness is only beginning," he said.

CNNMoney's Jackie Wattles contributed to this report.