"Major slump" refers to a significant decline or setback in someone's performance, productivity, or mood. It suggests a considerable drop or decrease in their abilities, accomplishments, or overall well-being. Full definition
If you doubt that, go back to the last major slump, the near 60 % decline in the Standard & Poor's 500 index from early October, 2007 to early March, 2009. (realdealretirement.com)
He resisted it because the field hit a major slump in the 1980s as experts moved to more promising areas of research — an AI winter, Schmidt called it. (entrepreneur.com)
Total real personal income has rebounded in the United States, but personal income less transfer payments is still in a major slump. (thinkadvisor.com)