second wind
a new feeling of energy after you have been working or exercising very hard, and had thought you were too tired to continue

[TahlilGaran] Dictionary of Contemporary English ▲

second wind
energy that is regained after being tired
After we got our second wind we continued on our hike up the mountain.

[TahlilGaran] English Idioms Dictionary ▲

second wind
n.
1. The easier breathing that follows difficult breathing when one makes a severe physical effort, as in running or swimming.
After the first quarter mile, a mile runner usually gets his second wind and can breathe better.
We climbed with labored breathing for half an hour, but then got our second wind and went up more easily.
2. informal The refreshed feeling you get after first becoming tired while doing something and then becoming used to it.
Tom became very tired of working at his algebra, but after a while he got his second wind and began to enjoy it.

[TahlilGaran] English Idioms Dictionary ▲