The poem begins like a small domestic story: a guest turns up in the night. But the details quickly turn uneasy. The guest "crawled on top of me" and "chose the best spot / to force himself in," language that sounds like an invasion, even a violation. The speaker is passive throughout. Things are done to them, and they can only watch.
The strangest detail comes at the end: eyes "so curiously mounted / on his shoulders," working their way "deep into me." That odd, almost insect-like description suggests the guest may not be human at all. Judging by the imagery, it could be a tick or some other creature that burrows into skin, though the poem never says so outright. It could also be read as a metaphor for something intrusive that gets under a person's skin.
The mood is creepy and quietly disturbing. The speaker's flat, matter-of-fact tone makes it worse, as if the horror is too close to fully react to.