What is the perception of the body?

I'm following the four foundations of mindfulness. This has given me round-the-clock body awareness. It can often be painful; but it can often be pleasant. The pleasantness is marred by its opposite. I notice from time to time the density of my body disappears along with all ideas of pleasant and unpleasant and their respective sensations. ## Questions ## Is the body a perception like all other perceptions? How does the subtle perceptions described in MN 121 translate into the body? - I'm asking this as there appears to be greater mental/emotional turmoil like an archaic or ancient frustration/restlessness.