I ask someone a question, but then realize I already know the answer. In English, I'd say: "Oh wait, never mind." What's 口语 for "never mind" in this context?
You can use 没关系 or 沒事.
To say "never mind" in general, you have a couple of choices. 算了 or 沒關係 both convey the general idea. 算了 however maybe be perceived as implying some level of impatience. In this specific context, 沒事 also works well.
But its mostly fine to use either, or both together as "算了，沒關係" (or "算了，沒事").
"mind" = "心意"
so my best translation
for "never mind"
is "不要 放在 心 上" , (bu-yao fang-zai xin shang)
i.e. "don't put (or carry) anything in your heart (mind)"
"別 掛心", (bie gua-xin)
"不 介意" (bu jie-yi)
Please note that, I always suggest using '心' or '意' in this case, because it catches the meaning of 'mind'.