我正要说到它，可是想不起来了。

I was going to mention it, but it slipped my mind.

《柯林斯英汉双解大词典》

我想不起来了—我当时一定是失去了知觉。

I can't remember any more—I must have lost consciousness.

《牛津词典》

“他叫什么名字？”—“我想不起来了。”

"What was his name?"—"I don't recall."

《柯林斯英汉双解大词典》

Put yourself in other people's shoes and I'm missing one, i can't recall which one I'm missing now.

学会换位思考,还差一个了,但是我想不起来还缺什么

耶鲁公开课 - 博弈论课程节选

because a lot of celebrities will be the kind of... What's the word? Can't think of the word.

因为许多名人将会是一种……这话怎么说？想不起来了。

英国的慈善事业 - SpeakingMax英语口语达人

gosh, I can't remember what it's called now, but it's essentially how our courts work

叫做……噢，我一时想不起来它的名字了，大概是关于法庭的运转，

哈佛法学院的课程 - SpeakingMax英语口语达人