Idioms and Phrases with not oneself
Not feeling physically or mentally well, as in I think there's something wrong; he's not himself, or She seemed to be improving last week, but she's just not feeling herself today. Also see feel like oneself.
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.