If a juror has personal knowledge respecting any fact in controversy, he must declare it in open court during the trial; and, if during the retirement of the jury a juror declares a fact as of his own knowledge which could be evidence in the case, the jury must forthwith return into court and such juror must, in either case, be sworn and examined as a witness in the presence of the parties.
Ala. Code § 12-16-7 (1975)