Amanda Billington, 33, was at a preview of the show Tree, created by Elba and Kwame Kwei-Armah.
The illustrator has regular seizures due to an undiagnosed condition.
But she came around on Wednesday to discover Elba was checking on her, before later escorting her to an ambulance.
She said: “I would love to thank him personally, but doubt I will cross paths with him, he’s very famous.”
The actor and director rushed to the aid of an audience member of his new play, Tree
It happened during the performance at Upper Campfield Market Hall, Manchester, as part of the city’s international festival.
Amanda, from Salford, was taken hospital and released after a check-up.