Incest and paralysis

A year after the loss of his only son, Takashi, his mother, Yumi, was unable to organize Takashi's room. However, today is Takashi's death anniversary...and when he gained the courage to enter Takashi's room, he was confused, and although he felt hopelessly sexy, he ended up masturbating. Moreover, when I feel like someone is watching me, my body suddenly becomes unable to move. "I can't believe this is sleep paralysis..." What is the true identity of the suspicious presence that draws closer to the confused Yumi! ?