I have not been getting enough sleep recently.  I am tired
sleep is a natural state of the body and mind . It restricts all your muscles and make you numb to everything around you so you can relax so please get some
Yes it is important to get enough sleep!
sleep is not same as wakefulness which reduces your being able to react to things around you. 
That is very true.  And there are varying levels of sleep
yes, they are known as non-rem and rem sleep