I had a 2x2x2 (vacant blocks) Hut built and with a bed, work table and furnace, leaving only a 1x1x2 block in which I can move in. At one point I decided to put a pressure plate in the last spot (next to a door). I went to bed that night and after I woke up my character was moving up and down and losing hp gradually, then I was told that I died because of wall suffocation. This was in HARDCORE Mode.
Edit: I played another hardcore game where I found that this has happened again, except this time the dimensions of the shed on the indoors was 3x3x2 (vacant blocks). I strongly believe that if there is no empty block on any adjacent side of the pillow side of the bed that the character gets forced into one of the sides and ends up suffocating on the object.