After becoming violent and biting a fellow traveller, the 24-year-old was restrained on board, before falling unconscious.
When the plane landed at Cork Airport after being diverted there, the young man was pronounced dead on the scene.
A post-mortem will now be carried out on the man, to establish whether he had an underlying medical condition, had a seizure or if there are other factors involved in his death.
On the same flight, a Portuguese woman was found to be travelling with amphetamines, and was questioned when she arrived at Cork.
It’s not yet known if the two things are in any way connected.
Irish flight operator Aer Lingus described the incident on Sunday afternoon as a ‘medical emergency,’ with all of the passengers on the flight being interviewed by police after landing.