expression, noun
empty nest syndrome
A psychological condition affecting parents when children leave home. Used in medical and everyday contexts.
末っ子が大学に行ってから、空の巣症候群になってしまった。
After my youngest went off to college, I developed empty nest syndrome.
Calque from English 'empty nest syndrome', combining 空の巣 (empty nest) and 症候群 (syndrome).