In dreams, gravity is a force that draws us towards the physical or material realms, rather than the spiritual, almost despite ourselves. As we wake up to the ordinary, everyday world, we can experience gravity as a tangible physical pressure.
Psychological / Emotional Perspective:
Emotionally, gravity symbolizes a lowering of emotion in dreams towards the more negative feelings of fear and depression. In such dreams there can seem to be an actual physical force present.
Everyday Material Aspects:
A sense of gravity can inject an aspect of seriousness into our dreams if there are problems or difficulties in waking life. These can be experienced as heavy or weighted objects.
Also consult the entry for Weighing / Weight.