“To the person in the bell jar, blank and stopped as a dead baby, the world itself is a bad dream”.
http://i.word.com/idictionary/bell%2520jar
bell Jar (noun)
:Bell shaped usually glass vessel designed to cover objects or to contain gases or a vacuum
Understanding what a bell jar is helps me to understand this passage better. The bell jar is really a metaphor for her “world”. The dead baby is of her spirit. not alive, suffication of her liberation. This spiritual death seemed more like a dream.