Falling forward and then paddling legs, what is it? :(

[Dudu]

Please help - have you seen anything like it before and what it is?
Bantam rooster, about 5 years old, in a good condition (not thin, on the contrary)
Yesterday was walking in a restricted way, kind of staggering a little, in the evening found him on his side with legs stretched to the side/to the back. Can't stand at all, falling over forward and then starts paddling (excessively) and biting the cloth in front of him (I believe this is a sign of pain, he is usually so quiet and sweet).
Still interested in food and water and actually very alert, even too much (stressed), not lethargic.
What could it be?

 

[Dudu]

Was searching on the forum here and found this video by another member - this is exactly how he looks, plus the frantic paddling after he falls on his side.... He has made it through the night but is still the same.

 

[Eggcessive]

His symptoms are neurological in nature. Many things such as Mareks disease, a brain inflammation from an infectious disease, a vitamin deficiency, poisoning from lead or toxin, and botulism could possibly be a cause for this. I would feed him chicken vitamins and electrolytes, and make sure that he can get enough food and water for now. Does he free range in a large area where he could have eaten something poisonous or tainted? Can you check your feed to make sure there isn't mold on it?

 

[Dudu]

Thank you so much Eggcessive, you are always so helpful!

He is still the same way and biting his thighs when I touch them, it seems it might be some pain in the muscles maybe?

I will try my best to take him to our vet to see what he says.

He lives in a crate with a hen (on sawdust bedding), I checked it and it seems ok (no mold in the crate). The feed seemed fine too but I will check more.

He is otherwise very conscious and very alert, and eats even though he is lying on his side. I help him drink and then the trouble begins, as soon as I pick him up he begins to paddle his legs excessively, though he is normally a very calm boy used to handling.