Dave Bonta's four lines turn sleep into a quiet journey. The title, "R.E.M.", names the stage of sleep when we dream, but the poem never describes a dream. Instead, it gives us a single image: the speaker sleeping like a boat that drifts over dark water and just touches the fish beneath it.
The comparison suggests that sleep is a kind of floating. The speaker is on the surface, but something alive moves underneath, a hint of the dreaming mind below. The phrase "without any thought going / through the dark water" adds to the calm. Nothing is being worried over or planned. The line break after "going" even makes the words drift a little, as if the sentence itself is moving.
The mood is hushed, peaceful and slightly mysterious. The speaker seems relaxed, even content, though the dark water leaves a faint sense of the unknown.