Advice on extent of injury, Scrub Jay (1 Viewer)

Hi all, I could not find an injury/rescue discussion on this forum but it's late and I don't have a lot of time.
I have a Western Scrub Jay that flew into a window in the interior of my friend's house this afternoon. It immediately went down and I folded its wings up and secured it in a box. I figured I could leave it for an hour and it would recover and fly off. Well it's been 5 hours and the bird now is in the following state:
-Alert, will drink water if beak held near tap
-Ambulatory. Will skitter across the floor if let free
-Unable to sit upright
-Unable to fly
-Can hang from my hand downward- very strong grip from talons
-Seems intact, no obvious wing injuries.

Can someone help me figure out what its injury might be? I've never seen this combination of symptoms before. I have rehabbed birds before and would prefer to do it myself if possible. Also seeing the other threads here, I will just say right now I will NOT club it over the head. I can freeze it, something I consider a much more humane method than clubbing and have done before.
I know it's just a scrub jay, but right now it's MY scrub jay.
Thank you all.

Hi kinglet and a warm welcome to you on behalf of the Staff and Moderators.

We have guidelines for you here. Do you have a rehabber's licence? Good luck and let us know the outcome please.

D