one's second wind
A renewed energy after a period of fatigue. I planned to stop working at 9, but then I got my second wind and just kept going. I'm sorry, but if I don't get a second wind soon, I'm going to bed.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
*one's second wind
1. Lit. one's stabilized breathing after exerting oneself for a short time. (*Typically: get ~; have ~.) John was having a hard time running until he got his second wind. Bill had to quit the race because he never got his second wind.
2. Fig. one's greater or renewed energy and productivity, gained at some time after starting. (*Typically: get ~; have ~.) I usually get my second wind early in the afternoon. Mary is a better worker after she has her second wind.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.