Romance of Two Worlds, A by Marie Corelli (1855 - 1924)

The book starts with a young heroine telling her story of coping with a debilitating illness that includes depression and thoughts of suicide. Her doctor is unable to help her and sends her off on a holiday where she meets a mystical character by the name of Raffaello Cellini, an Italian artist. Cellini offers her a strange potion which immediately puts her into a tranquil slumber, in which she experiences divine visions. This is the beginning of her journey to health, both spiritual and physical. (Summary by Wikipedia)