With head trauma, full post concussion syndrome shows up hours after the initial trauma. So *concussion* at this stage would make sense.
In a shaking, the brain gets jarred and that back and forth can cause coup and counter coup trauma...bruising on either or both sides of the brain. The delayed symptoms are due to swelling, which develops over time....I absolutely possible to survive a concussion. Lots of TLC, frequent but small feedings, electrolytes as @Amiga suggested, keep warm, and rest. If we are seeing a concussion don't be too alarmed if walking is effected (looking drunk or loopy).
Keep us posted!