code: function( dt ){
  
              if ( dt === true ){
                  // force sleep
                  this.asleep = true;
  
              } else if ( dt === false ){
                  // force wakup
                  this.asleep = false;
                  this._sleepMeanK = 0;
                  this._sleepAngPosMean = 0;
                  this._sleepAngPosVariance = 0;
                  this._sleepPosMean.zero();
                  this._sleepPosVariance.zero();
                  this.sleepIdleTime = 0;
  
              } else if ( dt && !this.asleep ) {
  
                  this.sleepCheck( dt );
              }
  
              return this.asleep;
          }
docs: Body#sleep( [dt] ) -> Boolean
  - dt (Number): Time to advance the idle time
  - dt (Boolean): If `true`, the body will be forced to sleep. If `false`, the body will be forced to awake.
  
  Get and/or set whether the body is asleep.
  
  If called with a time (in ms), the time will be added to the idle time and sleep conditions will be checked.