試験が終わって気が緩んだのか、風邪をひいてしまった。
Maybe I let my guard down once the exams were over, because I caught a cold.
孫の顔を見ると、祖父の頬が自然と緩んだ。
When he saw his grandchild's face, the grandfather broke into a smile.
勝っている時こそ気持ちが緩みやすい。
It's when you're winning that you're most likely to get complacent.