Now that we know that ghost pressing bed is a normal physiological phenomenon, it is much easier to explain.
I also have rich experience in this field, so I also have my own understanding.
Ghost press is an illusion and dream, which is mostly related to people's inner fears and desires.
The woman in red gauze kept throwing it at him, and then it turned gray at once.
This, I think, may be related to feelings, or emotional memory.
The red yarn represents warm and tender love, and turns gray, indicating the loss of enthusiasm and temperature.
This plot became his illusion, indicating that he was subconsciously worried about changes related to love.