Yesterday Oscar pulled a muscle in his neck region (we're not sure exactly where) while playing in a school field as he'd taken a good wipe out. He was fine all day and i assumed no injury but then last night he started crying/yelping when he'd try to lie down etc. We checked him all over and could only figure that he'd pulled a muscle as he didn't want to put his neck down to drink and/or lying down he'd yelp when lying his head.
I called my sister who used to work for a vet and she told me to just give him 1 advil and it would help relax his muscles and kill the pain etc. She said her vet used to tell people it was okay?! That was last night and he slept well and seemed better this morning, no crying or yelping while moving etc. So I'm assuming he's feeling better and we just need to be cautious not to let him re-pull the same muscle.
Anyways, this morning I didn't give him anymore Advil because I figured I should check the forum (I SHOULD'VE DONE IT LAST NIGHT!) and was shocked to find that it's considered toxic to dogs!!!

I could've killed my sister! I called her freaking out and she was like "well aspirin, tylenol, advil...all the same stuff?"
If he's fine 12+ hours later will he be okay?? He only had the 1 tablet.

Now Im really worried I"ve unintentionally poisoned him. He was back to his normal self this morning, had a good appetite and was fine when I left for work. What levels are considered toxic??