second wind
... that a second wind makes sleep-deprived persons feel less sleepy on the fifth sleepless day than they did on the fourth?
... that a <b id="mwAtw"><a href="./Second_wind_(sleep)" id="mwAt0" rel="mw:WikiLink" title="Second wind (sleep)">second wind</a></b> makes sleep-deprived persons feel less sleepy on the fifth sleepless day than they did on the fourth?