anyone know anything about voluntary nystagmus??? controlled eye shaking?!

When I was younger, I discovered I could shake my eyes, very very quickly, on command. I can't explain how I do it, it doesn't hurt; they vibrate, and I can move them fast horizontally (at the same time as vibrating them). I've met a few people along the way that "know someone that can do that!", and people generally find it pretty freaky. I was wondering if anyone knew anything more about this - I tried googling it, I only found what it is, "eyes vibrating" (I already know that much, I can do it).
I basically want to know the CAUSE of it, if it's HARMFUL in any way (although it doesn't hurt, should I not be doing it? Does it increase RISK FACTORS for anything?), & any FACTS about it.

No one in my family that I know of can do this (I haven't exactly asked everyone though), although I hear it can be hereditary.

ALSO, side note: I tried molly (ecstacy) a while back (judge me if you will), and once it "kicked in" my eyes INvoluntarily started shaking, much quicker than usual. My eyes would shake, then stop for a few seconds, then shake some more... This only happened for a minute, but it was weird because I usually have control of it and my eyes just went wild. While researching nystagmus I read that involuntary nystagmus can be caused by some drug toxicities, but that's never happened to anyone else that I've talked to that has taken molly...is that only because I can voluntarily do it, it just went out of control???

My only eye problems are nearsightedness and slight astigmatism. I don't know if this is correlated somehow with this, if the 8% of the population with this "condition"/freaky thing also have astigmatism or glasses/contacts.

Facts, risk factors, & most importantly causes???