"One more day" reads like a bargain the speaker makes with themselves: they will keep going, but only for now, and only just. The poem is about exhaustion and deep emotional pain, and it never pretends to be anything else.
The speaker describes a body and mind wearing down, with bones cracking and a brain rotting. Betrayal hurts like a stab in the back. Their bed feels like the only thing that understands them, which suggests how isolated they are. Other people look like ghosts, and life blurs into a dream that turns into a nightmare. The line about a voice that can no longer scream is especially bleak, since it suggests they feel unable to call for help.
The mood is heavy, numb and tired. Yet the final line, "but i'll be right there," leaves a thin thread of endurance. It's unclear whether it is a promise to others or to themselves, but it suggests the speaker is still holding on, however shakily.