Curiously after wearing push up bras my breasts create a flattened area where the padding of the bra was. What could cause this?

After taking off a push up bra I notice that there is almost a flat created under the breast where the padding of the bra is located. I notice this phenomena most in the right breast which is quite alarming as it appears that my breast is no longer round. After sleeping the entire night without a bra, it seems that my breasts have regained their normal shape. What could cause this? Implant type: cohesive silicone gel, tear drop shape, sub muscular. From an A to C, 6 months post op.