Nadyezhda Filaretovna von Meck was Tchaikovsky’s patroness.  In March 1877 she wrote of the effect of Tchaikovsky’s music on her.  The work being described is a Marche Funèbre on a theme from Oprichnik (this work is now lost).   

It is so superb that, as I had hoped, it elevates and transports me into a state of such frenzied happiness that I forget everything bitter and offensive in the world.  I couldn’t describe the disorder reigning in my head and heart every time I hear it.  My nerves are shaken by a thrill, I long to sob, to die, I have visions of another life, not the one all men believe in and wait for but quite another life, inaccessible, indescribable.  Life, death, pain, joy all disappear as I wing my way above the earth, my temples beating, my heart palpitating madly, my eyes misted so that I can see nothing and hear only the magnificent, enchanting music.  I forget the exterior world, I feel only the beauty it has to offer, I dread to waken from the spell.  My God! what a great man he is who can give me such moments to a fellow spirit. 

Cited in: Hanson, Lawrence and Elisabeth (1965) Tchaikovsky: A New Study of the Man and His Music.  London: Cassell & Company, p.153.