The CIA has played down the idea that the phenomenon is due to attacks by a hostile foreign power.
A declassified report seems to dismiss the idea that Havana Syndrome is caused by microwave weapons.
One of CIA Director Bill Burns's team members was inexplicably targeted during a recent trip to India.
Cases of unexplained illness among US diplomats are now being investigated by the authorities in Austria.
Directed energy attacks (or 'Havana Syndrome') are far more widespread than had been previously reported.
Two cases of what has become known as 'Havana syndrome' are being investigated by federal agencies.