Can flagyl cause hypertonicity & limbs/face numbness as side effect? was also taking percocet, benedryl, phenergan, (promethazine) synthroid, & klonopin w/no issue.

Rule out alcohol: Flagyl can cause a build up of a toxic substance if taken with alcohol. The alcohol can be consumed or can be assimilated by hand washes, mouth washes, etc. The toxic build up would be my first guess as to the reason for the side effects noted. With a pharmacist or online you can search for known side effects of Flagyl (metronidazole).