feel off

Mieko Kawakamiの小説 "All the Lovers in the Night" を読んでいます。

"With someone from our class?" I asked.
"Remember that guy Yoshii? I never really talked to him before, but seeing him there, after all that time, he was so easy to talk to. It was crazy. Like meeting a new person, but not. Reunions are stange that way."
"Does your husband know?"
"Maybe he does, maybe he doesn't. I bet it's the same for him. He knows that facing the facts won't change anything, so we might as well keep going. But something definitely feels off. On some level, it doesn't feel real. I mean, I'm still seeing Yoshii. It's fun.

上の引用文中の "feels off" の意味が辞書を引いても分かりません。　そこでChatGPTに意味を訊ねました。

ChatGPTの回答
In the context of the sentences you provided, "feels off" is used to express a sense of uneasiness or discomfort. When the speaker says, "But something definitely feels off," they are indicating that there is a peculiar or unsettling aspect to the situation. In this case, the speaker is describing a reunion with a person from their past (Yoshii), and despite the enjoyment and fun they experience, there is an underlying feeling of discomfort or strangeness.
The use of "feels off" suggests that, despite the surface-level enjoyment and the casual attitude expressed by the speaker and her husband, there is a recognition that the situation may not be entirely normal or straightforward. It conveys a subtle sense of disquiet or unease about the ongoing relationship with Yoshii and the impact it might have on the speaker's marriage.

なるほど、意味は分かりましたが、 "feels off" が慣用句なのかどうかを追加質問しました。

While "feel off" may not be a fixed idiom, the phrase is a colloquial expression commonly used in informal language to convey a sense of something being not quite right, uneasy, or out of place. It might not be as formalized as some idioms, but it's widely understood in everyday conversation, especially in English-speaking communities.
The use of "feel off" is not exclusive to American English; it is used by English speakers in various regions. People might say that a situation "feels off" when they sense that something is amiss or unsettling, even if they can't pinpoint exactly what it is.
It's worth noting that language is dynamic, and expressions like these can vary in popularity and usage across different regions and communities. In the context you provided, the use of "feels off" effectively communicates the speaker's sense of discomfort or unease in the situation.

"feel off" を使いこなせれば母国人なみですね。