Why do some people become more aggressive when tired?
From Poor sleep as a potential causal factor in aggression and violence



  In most people poor sleep will not evoke actual physical aggression, but certain individuals, such as forensic psychiatric
  patients, may be particularly vulnerable to the emotional
  dysregulating effects of sleep disturbances


  The relation between sleep problems and aggression may be mediated by the negative effect of sleep loss on prefrontal cortical functioning. This most likely contributes to loss of control over emotions, including loss of the regulation of aggressive impulses to context-appropriate behavior.


  Other potential contributing mechanisms connecting sleep problems to aggression and violence are most likely found within the central serotonergic and the hypothalamic-pituitary-adrenal-axis. Individual variation within these neurobiological systems may be responsible for amplified aggressive responses induced by sleep loss in certain individuals.