A character who reaches 0 magic points  or who has 2 or fewer hit points left goes unconscious.  So does a character who loses half or more of his hit points from a a single wound or blow and whose player cannot then roll CON or less on 1D20.  Unconsciousness lasts from one combat round up to the time needed to regenerate 1 magic point or 2 hit points, as applicable.  A successful First Aid or Medicine roll may return a character to consciousness.