I have exact same experience two days ago. It started with a small dot (2-3mm at 30cm distance). Soon it became a circular (prismatic, more like a C letter covering from 11 o'clock to 4 o'clock). Later it became whole spread on the right side of the vision. Lastly it just disappeared.
Hi,
How are you? Are there other symptoms present aside from the vision problems? You may benefit from imaging studies and from another evaluation by a neuro-opthalmologist, which specializes or deals with portions of the nervous system related to the eyes. Take care and do keep us posted.