Stumbling-something wrong

Hey guys, I am writing in even though this problem involves our collie, Lad. He will be 3 next month, and he is having a problem. This started all of a sudden and was noticed after we got back home on Saturday from being out of town. We went to see about the dogs in the yard as soon as we got home about 3 in the afternoon. We have someone caring for them twice a day, and she says she noticed no problems with him. It was hot, but not the hotest day, and they had fresh water in the shade. It was immediately obvious something was wrong. He was walking like a drunk and couldn't lift his leg to wee without losing his balance. The problem seemed to be in his rear legs mostly. Not sure what it could be, I suspected the heat had gotten to him (though we have two giant shade trees and a shaded porch they lay under when outside), even though this hadn't happened before. We took his temp and it was 102.9. We wet him down real good and brought him in to sit in front of the fan anyway. He drank, he ate, he acted his normal self, and he rested inside. He still seemed a bit wobbly in the rear, but way better, so I thought we'd found the problem, and that it was the heat. He slept outside Saturday night (he prefers it outside) and then I brought him in before the heat started Sunday morning. He spent most of the day in, with short 5 to 10 minute intervals in the yard, where he ran and played with our other dogs and seemed to have normal coordination. He slept out again Sunday night, but this morning when I went to bring him in again, he could hardly walk a straight line and could barely get up the 8 stairs to the porch. He staggered into the wall and was definitely having major trouble. We checked his temp, and it was 102.4, so fine there, according to the vet. SO, we carried him in to the vet immediately and they are keeping him to run x-rays and some bloodwork to check liver function in case he has a spinal cord injury or has injested a toxin. We do pull small ticks off occasionally (woods right behind the backyard fence) even though the dogs are on Advantix, and I did pull two small, not engorged ones off when we got back from the trip. The vet doesn't want to rule out tick-borne illness at this point.
Has anyone else here had anything like this happen?
He walks like he is a bit drunk and when he sits, he weaves slightly side to side. His rear toenails drag the ground frequently while walking (didn't do that before, and they are clipped to proper length).

UPDATE- Receptionist at the vet just said that she doesn't know what it could mean, but that he does have elevated kidney enzymes. Waiting for a call from vet

Oh God I am so sorry to hear about your boy Lad I don't know anything about elevated kidney enzymes, but I hope they can get him sorted.
Sending lots of healing thoughts to Lad and big :hug:'s to you . Keep us posted on how he's doing.

well, we are home from the vet, not any wiser, but several hundred dollars poorer. The vet took xrays that showed, possibly something abnormal on the spine, like perhaps a slipped disk, but can't be sure. The kidney enzymes being elevated were puzzling, too. We have been sent home with instructions to bed rest Laddie and he is on antibiotics in case it is a tick-borne illness, anti-inflammatories, and pain meds in case it is his back. We recheck kidneys and re-evaluate in 3 days. I dunno. They want him to take it easy in case it is his spine. Wish I had a clearer picture of what is going on with him. I do hope he improves and this is a temporary setback.