Guinea Hen with Spasms and Shaking

I have a 2 year old guinea hen who I found in the yard last night while locking up. His head is shaking and he is unsteady on his feet. I got some water down his throat last night and honestly thought he wouldn't make it through the night, but he is still here. He is not eating or drinking on his own and he is absolutely TERRIFIED when I handle him so I have been keeping that to a minimum.

Does anyone have any ideas?? Do guineas get Mareck's? I have always found them to be such hardy birds so I am baffled by his illness. Nothing has changed in his environment and no one else in the flock is sick. I am really hoping for the best but mostly am not sure as to whether to leave him on his own in the dark and quiet of sick-bay, or to try to administer electrolytes, water, etc, to see if he improves. Its a tough decision to make since he stresses so badly when handled.

Anyone ever have any experience with this?? His head trembles and he looks sky-ward at times. Its as though he has a neurological problem.