Immediately consult ophthmologist  as well as neurologist or higher institution where there is neuro-ophthalmology Dept. SGPGIMS Lucknow  is having best Neuro-ophthalmology in India

You mean total loss (not seeing even light) or hazy vision. It is a serious affair . Loosing  for 30 min is very long and recovery is poor. Was it in both the eyes or one eye  .In any case get a thorough proper eye examination from an eye specialist MS. Also a Neuro he will refer you to as these are mostly from Neuro causes. A thorough systemic exam by MD physician is mandatory beside cause finding investigations to find out the cause and for specific treatment. Don't delay it can be serious.

Hello there.  I can understand your concern.  No its not normal. Do you have high blood pressure? if yes, then are you taking medications on a regular basis? Kindly consult a MD consultant physician in person for further evaluation and management.  You can also consult a neurologist. Best regards. Dr. Anil kumar jain. Bangalore.