瘫软

mǔ qīn kàn dào ér zi chū shì yī xià zi jiù tān ruǎn le

母亲看到儿子出事，一下子就瘫软了。

The mother collapsed on seeing what had happened to her son.

hún shēn tān ruǎn

浑身瘫软

feel weak all over

shuāng jiǎo tān ruǎn

双脚瘫软

feel weak and limp in one's legs

tā méi yǒu zěn me zhēng zhá jǐ miǎo hòu tā zài tā huái li tān ruǎn xià lái

她没有怎么挣扎，几秒后，她在他怀里瘫软下来。

She had not struggled much and after a few seconds he felt her relax limp in his arms.

rú jīn zhǐ yào tā yī xià chuáng jiù cháng huì tān ruǎn zài dì wú fǎ hū xī

如今，只要他一下床，就常会瘫软在地，无法呼吸。

Today, when he leaves his bed, he often collapses and unable to breathe.