How to tell if your cat has a concussion?

I have a kitten, I'm not sure how old she is because I got her from a parking lot about 2 months. Anyways, tonight we let her outside and my brother came inside and said she fell from a tree outside which was over a truck, and we aren't sure if she hit it or not. She won't hardly open her eyes so I can't check her pupils and she's usually very very playful but all she wants to do is lay down. She walked a little but not much and when she did she started to tilt. It's 2:30 am so we can't take her to a vet yet, I just wanted to know if there was any other ways to tell what exactly was wrong with her?