The speaker seems to be caught in memory, and the title, "Stuck in the past," says so outright. The poem opens in the middle of an action: writing letters to someone, presumably a lover or someone missed, though the poem never says who she is. The speaker then describes a kind of lazy retreat. He sleeps on silk and refuses to go out, as if the world beyond the room has lost its appeal.
The final image is the heart of it. His mind turns to amber "like the evening." Amber is fossilized resin, and it traps things inside it, preserving them while holding them still. So the speaker's thoughts are thickening, warming and hardening around his memories. The evening light and his mental state blur together.
The mood is soft, sensual and a little sad. There is comfort in the silk and the golden glow, but also a sense of paralysis. He is preserved, but he is not moving forward.