“如坐针毡”，汉语成语，字面意思是“像坐在插着针的毡子上（as if sitting on a bed of needles）”，形容心神不定，坐立不安（feel extremely uneasy）。
“如坐针毡”与英语俗语“like a cat on a hot tin roof/like a cat on hot bricks”意思相近，都可以表示“be anxious and unable to sit still or relax. ”。
She's waiting for the doctor to call with her test results, so she's been like a cat on hot bricks all day.
After receiving the threatening phone call, he became extremely alarmed and fidgeted all day.