Not sure if I know what you mean by "silent" migraine, but I've had several ocular migraines over the years which is possibly what you're referring to. No pain at all, visual auras only, lasting maybe a half hour from start to finish. Starts with zig zag lines quivering in the center of my vision, then the quivering zig zags spread across my entire vision before eventually going away. I have a little nausea with them, but I blame that on the visual disturbance - like getting carsick.
The first one I had happened at work (at a doctor's office) and occurred after taking my first dose of a new prescription (antidepressant). With that one, the center of my vision just disappeared, like a black hole in everything I looked at, about the size of everyone's face. It only lasted about 15 minutes. I told my boss, a doctor, and he said I'd had an ocular migraine and not to worry about it, but not to take anymore of that medication.
After that, every few years I've gotten one with the quivering zig zag lines. I never knew anybody else who got ocular migraines until I mentioned it to my brother, who said he's had a couple, too. I have fibromyalgia but he doesn't, so I don't connect the visual disturbances to my fibromyalgia.