Help with a context sentence with 一気

[plantron]

Question about 一気

I love the context sentences! Sometimes the link to the given meaning is obvious, but often it’s like a riddle. This one for 一気 “one breath, one go, one sitting” has me stumped. Help me solve this riddle! 元気そうな父のかおを見たら、一気に気がぬけました。 It was such a relief to see my father, who looked well.