Skeleton On The Sea Floor -- revision

[Achebe]

It just appeared there one day, fused to the seabed ...I presume the 'it' is a reference to the 'skeleton on the sea floor'
as one clinically depressed merges with their mattress ...love 'merges with their mattress'
or decomposes into couch cushions. Weight fell .....a skeleton is not an image associated with decomposition. The flesh has already fallen away.
like a thick blanket over their face as they slept, ...I'm not clear now what is being talked about. Weight fell 'like a thick blanket' - so it's not actually the weight of the blanket. So what is it 'the weight' of and who are they? Can't be 'skeleton and seabed' since a seabed doesn't have a face...
convincing the mind to keep dreaming and the lungs to surrender.  .....a great image but the ambiguity above spoils it for me
It just appeared there one day, like a woman
of thirty-five suddenly seeing her feet wearing sensible heels, .....beautiful line. I'm confused about what the 'It' is now, though.
sitting behind a desk with a picture of a husband and two kids,
unable to breathe. ...lovely

I like the original images and similes you've used throughout the poem. 
I also like 'fused to the seabed', 'merges with their mattress', 'convincing the mind...surrender', and everything from 'like a woman' onwards.
By the end of the poem, however, I am not sure what the 'It' is.