A man died on board an Aer Lingus flight from Lisbon, Portugal to Dublin, Ireland Sunday after being restrained by crew members and falling unconscious due to an apparent seizure.

The incident occurred on Sunday when a man, who is believed to be Brazilian, inexplicably began to act violent mid-flight and attempted to bite at least one fellow passenger, reported The Irish Mirror. A pilot reported to controllers that the man had "injured one or two passengers."

The man then allegedly appeared to suffer a seizure and was then restrained at the back of the plane when the incident truly became disconcerting for passengers.

"After that it got worse I would say, his seizure seemed to get worse. He was actually on the ground shaking violently," said fellow passenger John Leonard.

"The noise he was making was like something I have never heard before," he continued, according to The Independent. "It's not something you'd hear everyday. It was like deep anguish is the best way I could describe it, very, very troubled. Not screaming in a sense you know if you'd hurt yourself or something, just a very guttural, from deep within him."

After the outburst, the rampaging passenger fell silent and became unconscious, prompting the pilot to make an emergency landing in Cork, Ireland.

While it's unclear exactly when he died, the man was declared dead shortly before 6 p.m. after landing, The Guardian reported.

"Horrible. I would say a very violent end - to die that way in the back of an aeroplane, it's not right. It was not very pleasant at all," Leonard said.

Authorities arrived on the scene and questioned most of the passengers and crew, while the passengers who were injured were taken to the hospital. The remaining passengers stayed on the plane for two hours and were then transferred to Dublin by bus. 

Aer Lingus classified the incident as a "medical emergency" but has failed to go into any greater detail beyond that.