Experiened those twice myself. 1st time 20 years ago, right after my divorce. No doubt brought on by stress. Last one I had was a few months ago, no divorce this time, but a stressful period for other reasons.
As with Casual, first time. I nearly shit a brick. I was sure it was a stroke! BIG blind spot in my vison that looked like a ragged hole torn in my field of view. Drove myself to the ER. DOC there had NO clue what it was. Found out years later at eye exam.
Good luck! (...and look into some stress reduction!)