I like the connections between the darkness. It plays into the ending, the idea of being buried alive you obviously can't see so it holds a lot of power and sets a dark tone to the poem.
I also like the subtle rhyme throughout the poem. It works very nicely. It isn't the most obvious of rhyme but once you get into the rhythm of the poem then you can feel around and find the rhyme in a nice way.
Also, it flows very nicely.
Also like the paralleling between the beginning and the end. Talking about days. The darkness in the beginning and then the almost yearn for the light of day again at the end also intensifies the dark feeling throughout the poem. Nicely done.
I like the title. Ties really nicely with the last sentence. Also, the word decay.