Sarah's "sleep" begins with a sense of being overtaken. The black cloud that used to hang above the speaker's head has come down and settled on them, pressing on their chest until breathing feels hard. The word "finally," repeated twice, is striking. It sounds less like panic and more like a grim relief that the waiting is over.
The last three lines shift the tone. The speaker stops talking about the cloud and talks about their soul, calling it "she," as if it were a separate, tired person. "Let her sleep" can be read gently, as a plea for rest. But sleep here is tangled up with suffocation and giving up, so it also carries a darker possibility, which the poem leaves unspoken. The mood is heavy, quiet and resigned. Short lines and plain words make it feel worn out, like someone with no energy left to argue with the feeling. If the poem speaks to you, it's worth remembering that this kind of exhaustion is something people can and do get help with.