Lizzy's poem begins like a child's fear of the dark, with a monster under the bed, but it quickly becomes something stranger. The monster lives "in my head," and the speaker asks whether she should be dead. That suggests the creature stands for something inside her, perhaps a dark mood or painful thoughts, rather than something lurking in the room.
What makes the poem unsettling is how warmly she treats it. The monster feels pity, gets witty, and makes her giddy. They fight and make up like old friends. Other people tremble and keep their distance, while the speaker finds comfort in its whisper and even a "goodnight kiss." Yet laughing and crying blur together, and thoughts of dying keep creeping in.
The ending is a farewell. She thanks the monster for serving her "through torture and pain," then says goodbye, leaving her in the rain. The mood is a mix of playfulness, loneliness, and sad relief, as if she is losing something that hurt her but also kept her company.