Wall Street’s CBOE Market Volatility Index (Vix) aka the Fear Index crossed the 19-level for the first time since 10 March thanks to jitters in the global market including Brexit concerns.
Vix, a yardstick for measuring fear or volatility in financial markets, added 2.56 points or 15 per cent to 19.59.
Factors that affected the index include the UK leaving the EU and it leading to destabilising trade in Europe.
Other worries include a slump in Chine crude oil futures and results of central bank meetings by Federal Reserve, Bank of England and Bank of Japan due to take place later this week.
Meanwhile, a study by economists has found that Sterling's value against the dollar could fall to between $1.30 and $1.10 if Britain votes for Brexit on 23 June.
Efficient Frontier Consulting's Iain Clark and Thalesians' Saeed Amen argued in their paper that Sterling could see itself in a crisis similar to what the Swiss currency faced in January 2015.
“In the event of a leave vote, we would expect a very high degree of volatility as GBPUSD moves well below 1.30, much as happened in January 2015 after the EURCHF defence level of 1.20 was breached,” the pair wrote.