[Tanush123]

Use a timer or use onplayerupdate ( i think it will work)

pawn Код:

new Float:phealth;
GetPlayerHealth(playerid,phealth);
if(phealth < 51)
{
    //apply the fall animation 
    TogglePlayerControllable(playerid,0);
    SendClientMessage(playerid,-1,"You have falled to the ground because you are injured");
    return 1;
}

try that