This is a very intense piece, romanticism at the maximum. In English it is called "Love Death". Dying for love, is it supposed to be sad? I am not sure... Not if you are a lover.
So, it is the final piece played at the opera called Tristan und Isolde; and it is sung. But here is the orchestral version, which I prefer over the sung one.
I think I have listened this piece 100 times in the last days, as it is so delightful.
And after being searching and listening for many versions, I found this one:
Which is the Liszt transcription to piano, but it is not played as pianists