If you google "writer's block" you will find that there are even people who deny its existence.
As a non-expert I do not know about that but I do know for sure there is nothing coming out right now for me. It is very frustrating because everything I do manage seems wrong or silly sounding. Continually restarting is very tiring.
I have heard it is a good idea to just write anything on any subject just to get the juices flowing. Even a poison pen to someone to get your emotions working (just DO NOT send it!). Or try some fun things like writing poems you might remember.
Another possibility is to lower our standards. Perfectionism can be very destructive of goals and deadlines. Relax a little. Work that meets lower standards is at least something accomplished. It is much better than a perfect blank.
From what I understand, most of the great authors have cold spells when nothing works. The problem is to not let yourself get discouraged and give it all up.
I bet the morning will be there to wake us up tomorrow as it always seems to.