be/feel under the weather
生病；觉得不舒服

have a splitting headache
头痛欲裂
When i study i have a splitting headache!
我学习的时候头特别痛！

take a turn for the worse
突然恶化
My headache is taking a turn for the worse.
我的头疼正在恶化。

black and blue
青肿的，瘀血的
His arm was black and blue.
他胳膊青一块紫一块的。

look/feel like death warmed up
看起来／感觉病得不轻
He shouldn't be working when he's so ill -- he looks like death warmed up!
他那么不舒服就不应该上班--看样子他病得不轻！

pop your clogs
死，死亡
I think I'll leave all my money to charity when I pop my clogs.
我觉得我死之后会把钱捐给慈善机构。