Screaming or howling

I do not remember that much of this one. It took place in some large building with a lot of corridors and rooms. Apparently, people started dying, falling asleep or disappearing, one by one. I immediately knew that some sort of otherworldly monster was present in the building corrupting people. Because the leader of the building kept telling everyone that everything was fine. But I had a vision of what happened to a victim. An ugly alien-like thing chose him. I cannot remember clearly, but I think the monster possessed him and walked him to his house where he was put in his bed, dead and deformed or something. His mother entered the room. She would not notice, but as she bent over the bed to look at her son, her body would morph and twist in weird ways. Her stomach became as thin as an arm and so on. She started screaming. I saw another boy walking around alone in the building, stopping in front of the monster that was completely still. The monster opened its mouth and quickly, the boy disappeared into it. I and everyone in my class came up with a plan. We would all sleep in one room in the basement, because it made us feel more safe being many there. After a while, I told everyone that we had to kill the leader, because we knew everything was happening because of him. I and my friend, <PERSON>, took some knives and sneaked into the room where all the teachers/leaders/whatever-they-were usually were. <PERSON> was ahead of me, eager to kill him. But as he entered, I heard an "oh no". I entered and saw everyone in the personnel sleeping a deep sleep that cannot be interrupted. I knew that being in their presence would "infect" me, because I did not lay low. I remember the monster coming after me later, and that I accepted death, hoping there would be something after it that would be better than fearing the monster all the time. I woke myself up and was happy it was only a bad dream.