C.M.
When I was late in my pregnancy and while nursing I had a couple incidents of a "visual migraine" which involved weird flashing lights, tunneling in, and loss of peripheral vision - these lasted about 15 minutes - I didn't have any pain. Like you I immediately thought of preeclampsia but also had none of the other symptoms. The next day my OB/GYN was ready to send me off for neurological testing - but that doc knew right away what we were dealing with. But, I'd call your doc again - this is not a time to fool around.