The idea of SoSa is you play it while you have quite a bit of hp still so that you are not taking damage any more. Don't think of it as a card that is meant to heal you back up when you are low on hp, that is completely wrong. It is used at high hp, and you take damage, and if your opponent doesn't heal you up for that amount of damage, then you played it at a bad time, oh well, if you get back to 100%, play another one after that. It's basically 2 turns of complete invulnerability without your opponent being able to cancel the effect.