Headaches, dizziness, nausea, hearing loss, and even cognitive difficulties reported by diplomats and intelligence officers starting in 2016.
Initial cases occurred in Havana, Cuba, leading to the name "Havana Syndrome."
Incidents expanded beyond Cuba to include China, Russia, the US, and other countries.
Theories point to directed energy attacks, possibly microwaves, but no conclusive proof exists.
Victims struggle with lingering health problems that are difficult to diagnose and treat.
The attacks raise concerns about the safety of personnel serving abroad.
Debate rages over whether the syndrome represents deliberate attacks or has a more mundane medical explanation.
Scientists scramble to identify a cause and develop countermeasures.
The possibility of future attacks leaves those in diplomatic and intelligence communities on edge.