-YnaAr
Happens to me fairly regularly. I think it's low blood pressure. My resting normal blood pressure is 90/40. When I'm stressed or ill the number can drop below this into an abnormally low range. If I don't eat properly, sleep properly or drink enough water I faint or get temporary blindness / deafness. It occurs most frequently when I stand up too quickly or when there's a change in air pressure (e.g. travelling on an underground train going up towards the surface or further down, going up / down in a long elevator, driving up / down a mountain, or descending / ascending in a plane that hasn't been properly pressurized).
I remain conscious throughout the episodes so I don't know if it's classed as fainting / passing out or not? I often lose the ability to stand up and I end up falling over or having to lie down with no motor control over my body but remain conscious. It's quite terrifying. Once I had vision and hearing loss for over 20 minutes and my extremities went numb (cut off blood circulation?) and then I suffered excruciating pins and needles when the circulation to them returned.
Doctors tell me it's nothing to worry about and dismiss my concerns. I feel that it really will be something to worry about if it happens when I'm driving one day and I crash and kill a load of people but hey ho...