Shelves over beds

I notice a lot of RPodders have put shelves over their bed areas and wondering how they're attached. I've lived all my life with earthquake faults (well, other kinds of faults too but anyway...) and would never put anything other than soft goods overhead or next to a bed. I can imagine a lightweight rack with soft goods on it, but only if it's attached so it couldn't bounce off it's mounting in a quake. Are people attaching them or just setting them on the valance? It's not the quakes the scare me, it's the idea of getting hit on the head that I find daunting