Hi....and welcome. Sorry surgery was not a positive experience for you....cerebral slump occurs when too much bone is removed by the surgeon and allows the brain to slump down further....
I had surgery 9 years ago this past May and I did not have this issue post op.
We have had several members that have developed this post op and typically another surgery is done to help cradle the brain to prevent it from slumping further where it could impinge the spinal cord or brain stem.