The title gives a clue: a hypersomniac sleeps far too much, and the poem puts us inside that heavy, tangled state. The speaker sleeps badly, then dreams "in my dreams," as if sleep has layers and there's no clear way out. Even waking up becomes something they only dream about. Real wakefulness keeps slipping out of reach.
The last image is the most striking. Waking is compared to "an open house / on a leaden street." An open house suggests light, welcome and movement, but the street outside is heavy and grey, like lead. So waking seems to promise life and warmth, yet it stays surrounded by weight and dullness. The speaker feels stuck, tired and a little detached, longing for a way out but not quite able to reach it. The mood is drowsy, quiet and faintly melancholy, helped by the short lines and slow, hesitant pace, which mimic someone slowly stirring.