The title of the song and the word used throughout the song is not easily translatable. I chose "Anguish" as it fits best in this case, but here's a quote from a Russian novelist: "No single word in English renders all the shades of toska. At its deepest and most painful, it is a sensation of great spiritual anguish, often without any specific cause. At less morbid levels it is a dull ache of the soul, a longing with nothing to long for, a sick pining, a vague restlessness, mental throes, yearning. In particular cases it may be the desire for somebody or something specific, nostalgia, love-sickness. At the lowest level it grades into ennui, boredom."