Bull Dog constantly whines and cries almost hyperventilating. Help?

Hey Everyone,

I've been boarding and house sitting for about a year now and have never had any dog freak out as bad as the 1 year old bull dog i'm currently boarding. Last night i played with him for about 2 and half hours just throwing the toy and getting some energy out of him so he would sleep well, i took him out and thought all was great and it was 10:30 so that was a good time for bedtime. I was wrong, he cried, whined, barked and was breathing so hard all night. I laid on the floor with him by a ticking clock (due to the sound being soothing) and he finally fell asleep for about an hour and then it was back to the whining and crying again and we were up the remainder of the night till this morning when i went to work. I believe he just has a really bad case of separation anxiety but does anyone have any suggestions of what i can do tonight for him to help? it's his last night with me and his owners come to get him tomorrow but i want to make sure he gets some rest i feel so bad when he just cries and i can't help.