気(き)のせいin one's imagination

母(はは)：「元気(げんき)ない？」娘(むすめ)：「いや、気(き)のせいだよ。」

Mother: "You seem down?" Daughter: "No, it's just in your imagination." {in one's imagination}

独(ひと)り言(ごと)：「地震(じしん)？！いや、気(き)のせいかもしれない。」

Monologue: "An earthquake?! No, it might just be in my imagination." {in one's imagination}

気(き)のせいかもしれないが、今日(きょう)の夫(おっと)は元気(げんき)がないように見(み)える。

It may just be in my imagination, but my husband doesn't seem to have much energy today. {in one's imagination}

雨(あめ)が肌(はだ)に当(あ)たったような気(き)がしましたが、それは気(き)のせいだったようです。

I felt as if the rain hit my skin, but it seems to have been in my imagination. {in one's imagination}

ママ友(とも)：「気(き)のせいだったらいいんだけどね、夫(おっと)が浮気(うわき)しているような気(き)がするの。」

Mom friend: "I hope it's just in my imagination, but I feel like my husband is cheating on me." {in one's imagination}