Question: During sleep there are five distinct stages. Brain activity increases from stages 1-4, even though you become harder to wake. This on it's own requires an answer. However, what really puzzles me is the fifth stage (REM), in which brain activity almost completely ceases and your body becomes paralysed, with your eyes shaking rapidly (hence REM (rapid eye movement)). Why does this happen and what is actually going on inside your brain at this time?