Brain herniation happens when swollen or shifting brain tissue gets pushed into spaces it does not belong. The squeeze can shut off blood flow and press on vital cables, so warnings appear fast and snowball. The first alert is a headache that spikes from bad to unbearable within minutes. It feels like the head is over-filled and may come with sudden vomiting that shoots out without nausea. Eye signs show up next. One pupil shrinks to a pin-point while the other balloons larger, and both may stop reacting to light. Trying to look side-to-side leaves one eye stuck in neutral.... Learn more