不小心摔倒了用英语怎么说

"Accidentally fell" 或 "fell by accident" 是表达不小心摔倒的英文短语。

I accidentally fell down the stairs. (我不小心掉下了楼梯。)
He fell by accident and broke his arm. (他不慎摔倒了，摔断了胳膊。)

这个表达来源于英语中的动词"fall" 和形容词 "accidental"。 "Fall" 意为 "摔倒"，而 "accidental" 意为 "偶然的，意外的"。将两个词结合在一起就能表达出"不小心摔倒"的意思。