I’ve found a new word, which at the moment sums up a feeling that I’ve not been able to put my finger on…
Toska (по-русский: тоска) – noun /ˈtō-skə/ – Russian word roughly translated as sadness, melancholia, lugubriousness.
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 of something specific, nostalgia, love-sickness. At the lowest level it grades into ennui, boredom.
Vladimir Nabokov, cited in A Field Guide to Melancholy by Jacky Bowring, HT: Maria Popova’s Literary Jukebox.