I'm not sure, but it sounds like he may have polio. If so, he needs thiamine, one of the B vitamins. You have to get thiamine from the vet but in a pinch you can administer large doses of B Complex. Polio is a thiamine deficiency and it can be brought on by stress. It causes some truly bizarre symptoms in ruminants.
If and when you find a vet ask him/her about polio. That is something sometimes even vets sometimes forget about. The treatment for it, thiamine, is cheap and the response is very rapid. If it turns out polio isn't the problem, thiamine can't hurt. The fact that he keeps falling down really sounds like polio though. Treatment needs to be started sooner rather than later. Good luck!!
Something else to consider is white muscle which is a selenium deficiency. It is very common in many parts of the country. A shot of BeSe will take care of that. We used to routinely give BoSe to our baby kids. I had forgotten about that. White muscle can cause weakness and falling down like you describe. It can also cause heart failure.