That first off sounds like possibly tetanus. :/ But proving it would be a matter for a vet. And probably too late by then if it is actually tetanus.
In case it's a deficiency here's a list to check through for matching symptoms:
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It's possible it's a snakebite case, or a bacterial/fungal/viral infection that causes spasming, or due to brain trauma... Has he been injured, bullied, or ill recently?
Toxicity perhaps?
Lead in particular but also other metals are ubiquitous in the environment and there's no safe level of it, only the level at which symptoms become a medical issue.
Are you reasonably sure his food and water and environment haven't contributed to any potential buildup of toxins?
Was he wormed or de-loused or anything like that recently? Vaccinated?
Best wishes. Hope he recovers.