Last night my Chiweenie Scooby played alot in our back yard with our Carin Terrier Shaggy. They ran alot, jumped, wrestled...early this morning he started to cry and acted like he couldn't get up on the bed (he has never had a problem before), he is not even 2 yrs old yet, then I went to take him out this morning and his back end collapsed. He started raising his right rear leg, everytime he drops it, he collapses again, I got some food and water in him and massaged his hips. He has started walking a little better, but he seems kind of "out of it" sometimes when I call him and when he lays down, he just kind of falls over, like he is completely exhausted. Should I take him to the vet or could it just be overexertion and I should let him sleep it off?