the enlargement of an organ or tissue because of an abnormal increase in the number of cells is known as

In fact it is not just nuclear fusion and fission that  can  transform  matter  (or mass)into energy. any time  energy  is produced, some small amount of  matter  or mass isconverted into energy.

Na+ loss through sweet plus the dilution has lowered na+ concentration outside of neurons, altering the na+ equilibrium potential. sodium exists more outside the cells than inside. when na+ is lost by sweat plus the dilution( because they drink a lot of water) changes the concentration outside the cell, forcing the water to enter the cell and attempt to balance the concentration inside/outside.the problem is that the abundance of water will cause the cells to swell. most cells can adapt, however, the brain cells can't that's why the runner has confusion and can't control the muscles.  if not treated and this occurs in less than 48 hours, it can be immediately fatal .