Thank you for taking your time to answer my question
He was on wellness which He currently hates
I am glad your cat is getting better.
Higher than normal dosing of flagyl can cause neurological symptoms. If the flagyl is very high it can even cause seizures, but at a slightly higher than normal dose it might cause him to be less active. But his decrease in activity may only be coincidental.
Once he is better please place him on a grain free canned only food. No dry food!