There’s a chance something is setting health back to above 0 by the next frame, causing the pain anim to play. since you already have a isDead boolean, maybe just add that to the conditions to check to play the pain anim.
if(Health > 0 && !isDead) {...
this way, the pain anim will not trigger as long as isDead is true, which if right you already set to true when health reaches 0 or less.