Hi, You want to play backwards the animation when the character start to fall down to the ground?, if that's the case you must use a function to change the animation.speed from a positive value to a negative value this way you can play an animation backwards.
Try to use a limiter to achieve this animation control if you don't your animation will be in loop, if your are using the loop wrapmode for your animations and don't forget to use the animation.CroosFade() to blend the animations.
Ok, solution is just simply remove "if(Input.GetKeyUp..." part. Animations finishes playing
and stops. It is very short animation so it does no matter it doesn't stop immediately. Most important is that my caracter doesn't freeze in strange pose. Anyway thanks for your answers AngryGerman and 3DMagicVR :)