My cat had a seizure then foamed at the mouth, and the hind legs are clearly weak
Expert Answer
A cat that seizes and then foams at the mouth is mainly considered to have epilepsy, poisoning, metabolic acidosis, low blood sugar, or encephalitis. Take the cat to a vet promptly for diagnosis and targeted treatment. Feline epilepsy is a nervous-system disease from abnormal brain neuron firing; it cannot be cured but can be controlled with anti-seizure medication.
Also, if the cat ingested a toxic substance, it may depress the central nervous system and disrupt nerve signaling, triggering seizures. In that case, prompt detoxification treatment is needed.
A cat seizing and foaming at the mouth is an emergency, full stop, I'd get to a vet now rather than wait. It could be epilepsy, but poisoning or low blood sugar can look the same and kill fast. Keep her somewhere dark and quiet, don't put your fingers near her mouth during a seizure, and drive. If this already stopped, she still needs an exam today, because whatever triggered it will likely happen again.