EXCLUSIVE
Louis Mandylor -- best known for his role as Nia Vardalos' brother in "My Big Fat Greek Wedding" -- is lucky to be alive after collapsing on the set of his new movie.
Mandylor was shooting scenes in 90+ degree heat Tuesday for the movie, "Daylight's End" ... when he became ill and was rushed to a hospital in Tyler, TX.
Doctors diagnosed the illness as heat exhaustion and dehydration -- which affected Mandylor's kidneys.They're saying kidney failure was on the horizon ... this according to Mandylor's people.
He's expected to recover and should be released from the hospital Friday.
