self-possessed
1. [ adjective ] in full control of your faculties
Synonyms: equanimous poised self-collected self-contained collected
Examples:

"the witness remained collected throughout the cross-examination" "perfectly poised and sure of himself" "more self-contained and more dependable than many of the early frontiersmen"

Related terms: composed
Similar spelling:   self-possession
  self-seeded
  self-confessed
  self-styled
  self-service