In evening while studying i started noticing some very bright patch( just like a sharp bright patch we see after staring at sun) in my left eye making it difficult for me to see at that point and then within an hour my entire left eye started causing more difficulty in seeing. Few minutes later my vision got normal and now my forebrain has started paining a lot..What might be the reason for all this...(I have had severe headaches previously also but they never affected by vision)