under the weather -【Cambridge Dictionary】: If someone is or feels under the weather, they feel ill,如果一个人感觉under the weather,说明这个人身体不舒服。under the weather产生于旧时代航行活动,那时候如果有水手身体不舒服,就会被带到甲板下面,免受恶劣天气(bad weather)的影响,有助于身体恢复,所以人在甲板下面,也理解为在天气(weather)下面。只要身体有点不适或者状态比较萎靡,都可以用under the weather。
I'm feeling a bit under the weather - I think I'm getting a cold.
我感觉有一点不舒服,我可能感冒了。