1
general::
Having one's wits about one, mentally competent, as in John may seem absentminded, but believe me, be's all there. This phrase is often used negatively, as not all there, for being without one's full faculties. For example, I wonder about Justin; sometimes it seems as if he's not all there. [Mid-1800s]
American Heritage Idioms
2
general::
Phrase(s): all there
Fig. alert, aware, and mentally sound. (Usually negative.) • After talking with Larry today, I get the feeling that he’s not quite all there. • You do such foolish things sometimes! I wonder if you’re all there.
McGrawhill's American Idioms And Phrasal Verbs