The twist the head and pop the neck is too aggressive for many subtle upper neck injuries. It's like using a shotgun to shoot an ant. It may help the lower vertebra but can cause inflammation higher up.

The activator does not force anything. It just sets the vertebra in motion with the muscles/tendons and ligaments pulling the vertebra into position. Even cranked up, it is gentle compared to the other. Low risk.

You don't likely have brain swelling. You have joint inflammation. It may put pressure on the blood vessels and reduce blood flow.

Chiro has little impact on the concussion other than allowing better blood flow by reducing inflammation.

You need to understand that you likely have two injuries. A concussion that has limited treatments available. And a neck injury that has many treatments available. But, you need to also take care of you neck. The chiro can't do his work if you don't follow up with good discipline to not aggravate the neck.

With the neck getting better, many concussion symptoms will be likely to improve.