A<unk>  or grey-out, is a transient loss of vision characterized by a perceived dimming of light accompanied by a brown hue and a loss of peripheral vision. It is a precursor to fainting or a blackout and is caused by hypoxia, a loss of blood pressure or restriction of blood flow to the brain. It is commonly experienced when suddenly standing up (see orthostatic hypotension), especially if sick, hungover, or suffering from low blood pressure or shock. Usually recovery is rapid and a<unk> can be readily reversed by lying down.
Brownout 
Sciatica
Shone's syndrome
Legius syndrome
Straight back syndrome
Barth syndrome
Bell's palsy
Carpal tunnel syndrome