get a/(one's) second wind

To experience renewed energy after a period of fatigue. I'm sorry, but if I don't get a second wind soon, I'm going to bed. I planned to stop working at 9, but then I got my second wind and just kept going. I better get a second wind because I need to finish this paper for my 9:00 AM class tomorrow!

get your second wind:

gain a new strength or energy to continue something that is an effort.

get your second ˈwind

(informal) find energy, strength or enthusiasm after feeling tired or after a period when you produce little: After midnight the dancers seemed to get their second wind and went on till dawn.

This expression comes from running; after feeling out of breath at the beginning of a race, you later find it easier to breathe.

second wind, to get one's

To proceed with renewed vigor after a lapse. The allusion here is to athletes who, after initial breathlessness, warm up and resume their regular breathing. In the early twentieth century this phenomenon was transferred to other kinds of undertaking in which, after an initial flagging of energy, one is able to continue with fresh vigor. Josephine Tey used it in The Franchise Affair (1946): “Perhaps it was the presence of an ally . . . or perhaps she had just got her second wind.”