Head trauma - please help

Saturday morning my 1 year old cat was hit by a car. My dad found him, luckly straight after it happen. He made it back into our garden. He was breathing heavily in a lot of stock. He tried walking to find a quiet place to hide but as he tried getting up to walking, he just kept flopping down. On the way to the vet he was still alert to what was going on. The vet rang later on that day to let us know there were no broken bone and he seem fine. He just had a little cut on his paw and a cut on his lip, like he had bite it.
It got to just before 8pm at night and we were in our way to pick me up but the vet rang and he had began to go down hill. He had coordination, every time he tried walking his back leg went wobbled and he had to lay down. Also he kept going bossed eyed and couldnt focus. So we left him at the vets over night.
Sunday morning he was still in the same way. The evening come and the vets rang again to let us know how he was etc. the vets told us the he keeps hitting and pawing at his head which is a sign of a head trauma, meaning swelling or a bleed on the brian
Today I popped into the vets to see him and give him lots of cuddle. It was heartbreaking at first to see him laying the wired up to a drip. Straight away he knew how I was purring away as I stoked him. But it seems he has now lost the movement in his back legs, the right more so then the left. He is also not eating apart from alittle bit of meat I gave him.

It's so strange that all these symptoms have began hours after the hit. Im trying so hard stay positive but there is a lot of worried.

Our kitten was hit on the head with a big glass jar and started seizing.  Shortly after she stopped breathing.  I was able to recessitate and rushed her to ER.   The ER Vet gave her Mannitol injections and she completely recovered.  But I think it is only effective if given within the first few hours after the trauma.  I would consult with the vet.

http://www.rxlist.com/mannitol-iv-drug/indications-dosage.htm

I agree about talking with the vet about Mannitol. But, as @Marsch21 has mentioned, I do believe there is a timeframe in which the medication has to be administered.

We took in a cat about 6 mo ago after he was hit by a car. His injuries were very similar to your cat (no broken bones, laceration on mouth, head trauma) that recovered fairly well after receiving Mannitol. This particular cat does have some permanent damage; BUT, he is fully mobile, eats, drinks, uses his litter box, etc all completely normal. His response time to things (like toys, sudden movements) is just slow.

Thank you both for your help. I will speak to the vet about Mannitol.

6 day on and he's still not better. He is now not urinating and there is blood in it. There is still no movement in his back right leg. And his temperature is up and down. One day is gods and he's more himself and the other day he's not I don't know what to do! The vets have no idea!

His bladder MUST be emptied or it will rupture---might already have.

This is a medical emergency. I don't understand why a vet would say they don't know what to do.

You may need to make some hard choices here and quickly but get a vet involved right now. Right. Now.

The vets are involved, he's been in there in Saturday morning...

He's at the vet? Good. Are they going to put a catheter in? Or did they and that's how they found the blood?

I'm so sorry you are going through this.

Did they give him mannitol?

Hes been lacking urine. And the be having to extract his bladder. Yerr he been on loads of drug. They think it's s underline problem the the accident has brought out. But they are confused what wrong. I've been visiting him everyday. One day he happy and him ( no moving) then the next day he's down with a high temperatures