SM, it sounds like an Ocular Migraine:
https://www.allaboutvision.com/conditions/ocular-migraine.htm
I get those about 3-4 times a year.
BUT, as others here have pointed out if this is your first time experiencing this, check with your Optometrist/Ophthalmologist to confirm that it's not the onset of a retinal detachment which is obviously very serious.
Mine typically last about 15-20 minutes and they are kinda FREAKY! But they do go away.
Cheers!