Defense Department Secretary Lloyd Austin has released a new memo urging Pentagon employees to report cases of Havana Syndrome, including the department's contractors.

Havana Syndrome was described as a mysterious neurological illness that sprouted years ago among U.S. personnel in Cuba, according to a CBS News report.

The memo noted that over the past several years, many defense department employees had reported a "series of sudden and troubling sensory events." The symptoms include headaches, nausea, and loss of equilibrium, with the cases happening predominantly overseas.

Austin said in the memo that one should immediately remove themselves from coworkers and/or family members from the area and report the incident and symptoms to their chain of command security officer.

Austin added that other affected persons, such as dependents, are highly encouraged to report suspected incidents.

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Havana Syndrome

Disturbing medical symptoms were allegedly first experienced by a team of U.S. Cuban Embassy workers in Havana in 2019.

A growing number of developments and staff working in other regions such as Beijing, Vienna, and Berlin have all reported the same symptoms seen in Cuba, according to a Gizmodo report.

Some of the symptoms reported were sudden, unexplained headaches, dizziness, and memory loss. This sometimes led to brain trauma and permanent hearing loss.

Two hundred people were the total tally of those affected, with 60 of those cases being Defense Department employees or their relatives.

Researchers claimed that the syndrome was linked to pesticide exposure and cricket calls, among others. However, federal officials have yet to come up with their own theories that cause the syndrome.

Officials theorized that it usually involved some sort of secret sonic weapon. However, medical and scientific experts refute the "weapon" theory, saying that such a weapon would need to break the laws of physics to cause some of the symptoms in Havana victims.

Michael Hoffer, the first medical professional to examine workers with the syndrome, was the first to suggest that workers may have been attacked by a "directed energy" weapon, according to a Military Times report.

Cold War-era surveillance technology was also among the factors being considered to have caused the neurological symptom.

Some American officials earlier noted that the technology was used by the G.R.U to eavesdrop but not to deliberately injure.

The officials noted that that later episodes look more like deliberate attacks by Russia's military intelligence agency, according to The New York Times report.

Rep. Adam B. Schiff noted in an interview that multiple nations could be involved, adding that it was important not to dismiss different explanations.

Schiff said that he thinks any of those explanations are feasible.

The House is eyeing a Senate-approved bill aiming to extend assistance to current and former government officials injured and suffering from the Havana Syndrome.

C.I.A. Director William J. Burns noted in July that one episode in Vietnam had temporarily delayed U.S. Vice President Kamala Harris' visit to the country.

Serious cases of the syndrome among military officials will be treated at Walter Reed National Military Medical Center, while those with less grave cases could be treated locally.

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Written by: Mary Webber

WATCH: New 'Havana Syndrome' Cases Reported By US Officials Across Globe - from NBC News