She is overtaken by a sensation of unbeing. There is no other word for it.

Disenchantment is a malady, and even if it is caused by particular circumstances, it is wise to overcome it as soon as possible. The more things a person is interested in, the greater their chances of happiness.

her eyes closed against some
unimagined darkness, where she is buried in an ache
in which nothing makes
sense.

There was too much, but every moment they were inside she was aware of the terrible danger they were in, and she had the distinct sense that her luck was now the thinnest piece of fragile ice, and they were edging out further and further over and abyss.

I have gazed into the abyss, and the abyss has gazed into me. And neither of us liked what we saw.

All her excitement had seeped away, leaving behind a terrible sadness, an emptiness that felt violent, as if she'd been gouged"

For Polletti, experience had brought only the bitter residue of pleasure which is the true essence of disenchantment. Certain delights which in his youth had seemed unique and unobtainable had turned out, upon acquisition, to be infinitely and drearily repeatable.

. . . disillusionment is often painful, you know

For a long time I had not approached the forbidden fruit called happiness, but it was now tempting me with a melancholy persistence. I felt as though Sonoko were an abyss above which I stood poised.

She searched the truth with an anguish almost as great as her terrible fear of finding it .

She was lost in her longing to understand.

An indescribable oppression, which seemed to generate in some unfamiliar part of her consciousness, filled her with a vague anguish...like a shadow... a mist passing across her soul's summer day.

For Madame Raquin, there was such a fathomless depth in this thought, that she could neither reason it out, nor grasp it clearly. She experienced but one sensation, that of a horrible disaster; it seemed to her that she was falling into a dark, cold hole. And she said to herself: "I shall be smashed to pieces at the bottom."

It was not so much shame that I experienced as the feeling that the actual world was an unfamiliar organism utterly unlike the world of my imagination. I was assailed by a sensation of desolation more intense than anything I had previously known, as if I had been abandoned at dusk in an autumnal wasteland where no answering sound would ever come, however often I called. Is that, I wonder, what is meant by the pat phrase "disappointed love"?