What is "to lose one's mind"

Mind \Mind\ (m[imac]nd), n. [AS. mynd, gemynd; akin to OHG. minna memory, love, G. minne love, Dan. minde mind, memory, remembrance, consent, vote, Sw. minne memory, Icel. minni, Goth. gamunds, L. mens, mentis, mind, Gr. me`nos, Skr. manas mind, man to think. [root]104, 278. Cf. Comment, Man, Mean, v., 3d Mental, Mignonette, Minion, Mnemonic, Money.]

1. The intellectual or rational faculty in man; the understanding; the intellect; the power that conceives, judges, or reasons; also, the entire spiritual nature; the soul; -- often in distinction from the body.

   By the mind of man we understand that in him which thinks, remembers, reasons, wills.
   --Reid.

   What we mean by mind is simply that which perceives, thinks, feels, wills, and desires.
   --Sir W. Hamilton.

   Let every man be fully persuaded in his own mind.
   --Rom. xiv. 5.

   The mind shall banquet, though the body pine.
   --Shak.

2. The state, at any given time, of the faculties of thinking, willing, choosing, and the like; psychical activity or state; as:

   1. Opinion; judgment; belief.

      A fool uttereth all his mind.
      --Prov. xxix. 11.

      Being so hard to me that brought your mind, I fear she'll prove as hard to you in telling her mind.
      --Shak.

   2. Choice; inclination; liking; intent; will.

      If it be your minds, then let none go forth.
      --2 Kings ix. 15.

   3. Courage; spirit.
      --Chapman.

3. Memory; remembrance; recollection; as, to have or keep in mind, to call to mind, to put in mind, etc.

   To have a mind or To have a great mind, to be inclined or strongly inclined in purpose; -- used with an infinitive. ``Sir Roger de Coverly . . . told me that he had a great mind to see the new tragedy with me.''
   --Addison.

   To lose one's mind, to become insane, or imbecile.

   To make up one's mind, to come to an opinion or decision; to determine.

   To put in mind, to remind. ``Regard us simply as putting you in mind of what you already know to be good policy.''
   --Jowett (Thucyd. ).