Demi Moore endured an illness while she was filming an upcoming horror/sci-fi movie. The actress, who has spoken about her health before, opened up about her experience in a recent interview. Hollywood icon Demi Moore, 61, divulged how intense it was filming “The Substance,” which is a movie she stars in alongside famous actress Margaret Qualley. Sitting down for an interview with a media outlet in London, where she was joined by Margaret and the film’s writer-director, Coralie Fargeat, Demi revealed that she had come down with something during production. An article written by Emily Zemler an…