Writing spell unceremoniously drags you out of your cosy sleep. Things that are ready to see the light of day need you to give them a form to exist. The sounds translate into words and keep pouring through your fingertips until there's nothing left to say.
Its unyielding power is bigger than you or anything else, bossing you around until the purpose is achieved and you may go back to sleep feeling unconsciously relieved. Until the next powerful tag overwhelms you to write again.