Bitcoin sank as much as 21% on Friday, extending its loss from its intraday high this month toward 40%, as the crypto-world was swamped by a wave of selling.The digital currency dropped to as low as $12,191.80 before trading at $12,975.50 as of 3:47 pm in Hong Kong. Bitcoin, which fell as much as 38% from its peak of $19,511, is still up more than 1,100% this year. Other cryptocurrencies also plunged, with bitcoin cash crashing 38% and ethereum losing 26% over the past 24 hours, according to coinmarketcap.com.Investors are having a “reality check”, said Stephen Innes, head of trading for Asia Pacific at Oanda Corp. “At the heart of the matter was a frenzied demand for coins with limited supply has now led to unsophisticated investors holding the bag at the top.”The plunge comes amid growing signs of mania for anything cryptocurrency related.