골치가 아프다

To have a headache from a complicated or annoying problem; used when something is mentally exhausting or stressful

내 코가 석 자다

Used when you're too overwhelmed with your own problems to help others; literally 'my nose is three feet long.'

눈앞이 캄캄하다

To feel hopeless or not know what to do next; literally 'everything goes dark in front of my eyes.'