Relax, my friend. If you accept the Many-Worlds Interpretation at all, then you're constantly splitting into parallel copies, millions of times per second, with every little decoherence event that takes place in your brain. Whether or not you use a quantum random number generator is totally beside the point. :-)

(But if it makes you feel less terrified, you could also choose one of the interpretations according to which "only our branch is real." As far as anyone can tell today, there are no consequences for any experiment we'll ever be able to do.)

Why would this only apply to using a quantum random number to make a decision?

Also, what do you find terrifying about the existence of multiple universes where every possible outcome of a decision you make plays out?

nvm i didn't want you to answer my question anyway