진선여고 부교재 두 문장 해석 부탁드려요

부교재에 나온 두 문장 해석 부탁드립니다.
“As a professional working for a large defense electronics firm, Stan found himself riding a roller coaster of concern about layoffs. Every few years, it seemed, top management slashed jobs as work slacked off—only to hire again when things started looking up.”