Even severe brain injuries may seem somewhat minor when they first occur. And trained doctors and nurses can have a hard time figuring out whether a brain injury is serious or not. Head Injuries: Short and Long-Term Effects: Some of the effects of head injuries are acute—that is to say, they last for only a short period of time. The acute effects of a head injury can include: Pain at the site of the injury. A “dazed” feeling. Pupils that are unevenly dilated. Memory loss (either short- or long-term). Loss of consciousness. Visual disturbances. Seizures.