An arc of black & white zig zags in the left side of view - formal term Scintillating Scotoma. Some people take drugs to get that effect, migraine sufferers take them to stop it.

Had one of those this morning too. I get #MigraineWithAura every couple of months - just the visual disturbance & dissociation, luckily no headache. #Sumatriptan inhaler, eyemask & earplugs helps. Useful to have #MigraineTrust migrainetrust.org advice too.