If you are experiencing something like a huge black thing in your peripheral vision that disappears when you try to look directly at it, it could be related to various factors.
One possibility is that you might be experiencing floaters. Floaters are tiny specks or strands that float in your field of vision and are more noticeable against bright backgrounds. They are often harmless and are caused by small bits of debris in the vitreous gel of your eye. However, it's essential to have your eyes examined by an eye doctor to rule out any potential eye issues.
Another possibility is that you could be experiencing visual disturbances related to migraines or other neurological conditions. In some cases, migraines can cause visual symptoms, such as seeing flashing lights or dark spots, even when not directly looking at them.
However, it's crucial not to jump to conclusions and self-diagnose. If you are regularly experiencing such visual phenomena, it is essential to consult a healthcare professional, such as an ophthalmologist or a neurologist, for a proper evaluation and diagnosis. They can assess your symptoms, take your medical history, and perform necessary tests to determine the cause of your visual experiences.
Please prioritize your health and seek professional medical advice to get a proper understanding of what you are experiencing.