I cannot tell you what pain I feel when I see how much my mother is under my father's thumb.

我无法向你形容，当我看到母亲完全在父亲的控制之下时我有多么痛苦。

《柯林斯英汉双解大词典》

In are the eye tears, what pain dazzling?

眼里的泪光，是什么痛的刺眼？ ？

youdao

In the past, what pain have I linked to doing it?

我把作这件事和过去什么痛苦联系在一起了？

youdao

"One thing I've learned over life is that you don't really know what pain is or joy is until you experience the other."

VOA: standard.2010.03.25

Yet somehow it was transformed into, what it's turned into, a beautiful thing, although not without pain. -Yes.

但您的一生却，得以转化成另外一种美，尽管伴随着苦痛，-是的。

普林斯顿公开课 - 人性课程节选

I won't get into definitions of what torture is but it would cause somebody tremendous pain and anguish to keep them from sleeping.

我就不解释什么是施刑了,如果不让人睡觉的话,会给人造成巨大的痛苦。

耶鲁公开课 - 心理学导论课程节选

What pain, what boredom, what insecurity has led them here?

FORBES: Seattle 'Superhero' Phoenix Jones Arrested on Assault Charges

Burns places automotive foresight at the intellectual crossroads between what the majority of consumers really want (or what pain they want to avoid) and what pundits and ideologues think would be a better solution.

FORBES: Nonsense futures of the automobile straightened out by some basic consumer cost-benefit thinking

So my best answer for your first question is that yes, ketamine might help your pain, depending on what type of pain problem you've got.

CNN: Is it safe to use ketamine as a pain drug?