Eh, you should say exactly how much is healed in the notes, so people don't assume it's a constant or random value. In addition, if people think it's OP, you can set its value to damage taken / 2 (rounded up) to maintain its low cost. Also, does its effect kick in when creatures are sacrificed?
Are you going to make a "masochism" card, with each instance of the player being damaged giving a random creature the player controls +1/+1?
About its OPness, the thing is that card deck doesn't really help you kill your opponent, it actually does very little to change the game for the 1/30th of the deck it hoards. I mean, even a Druidic Staff is more powerful.