headfirst
adv. 不顾前后地；头向前地
例句
He had apparently fallen headfirst down the stairwell.
他看上去是从楼梯井口头朝下摔下来的。
《柯林斯英汉双解大词典》
It is best to check the temperature of the water before diving in headfirst.
潜水前最好先检查水温。
Landing headfirst in the water, he felt his pulse quicken.
一头栽倒在水中后，他感觉到脉搏加快。
