To OP - did you read the symptoms of ocular detachment in the Mayo clinic report above. Do you have floaters? If you are having the flashing, or the field of darkness appearing, go to an emergency room.
Still worth asking about so that you know if you should worry if it happens again. (I'm the pp who thinks it sounds like an occular migraine). I wouldnt rush to the er right now, but I would call your Dr in the morning.
It could be something else and I would call your doctor right away. Every visit during my pregnancy I was asked if I had symptoms just like you described. It could be something completely benign but you would want to rule out anything else just to be safe.
Even though you feel fine otherwise, if it IS a detatched retina, the earlier you get it treated, the better your chances to not lose vision in the eye.
You can go to an ER and they will have someone who can look at the retina and see if there is any danger.
That sounds like it may be more like a retinal detachment than a pregnancy related issue? If so, you'll need to get to an eye doctor pronto. Is it one eye or both? If both, this is not likely.
Are you wearing contacts? Take then out and see if that helps.
One of my girlfriends said the first way she knew she was pregnant each time was that her contacts didn't fit correctly. Her Dr confirmed that some women have their eye shape change slightly.