Dog help! Can't stand up!

[Price]

Hi everyone, I'm new to the site and I didn't know where else to ask for help.
My dog, Ringo, who is around 1 years old is unable to stand up like he doesn't have the strength.
Thursday I found him laying in the yard not able to move like he was paralyzed. We got him up put him in the shade and gave him water. After a few hours he was able to stand and take a few steps but his back legs wouldn't work very well like he forgot how to use them and he would fall back over. Eventually he could stand on his own and walk just fine with a small awkward limp type thing where his butt would sway. Today, Saturday, He was doing the same thing just laying down breathing hard and panting. He can move his legs but cant stand on them like he has no strength at all. I did the same thing so far, carried him to the shade and gave him water. He's out there now. Any ideas of what happened? Or what I should do?
I have a theory of a snake bite but I figure more swelling would occur and there wouldn't really be a grace period where he could walk and get around fine.