An example of why I don't stress about having a control arm bolt coming undone because the head is facing downward. My Impala has a two piece driveline, and the carrier bearing has 2 bolts that hold it to the frame and they face downward. They don't have even a nut on the other side, they just thread into an 1/8" thick piece of metal and I have never had any issue with them falling out.
