I get that after I have a cold with a fever. It's weird but it's usually after some illness like that. First one eye then the other later or the next day. When I first saw it, I thought it was a detached retina.I have it occasionally...But some have it more often.....It's as annoying as the squiggle lines in your eye...It tinnitus of the ear...oh yeah...
Are people born with it, I've had for as long as I can remember. I just had it a short while ago
Which is usually caused by sinus drain.