Fainting or syncope can be caused by dehydration,
medications, diabetes,
pregnancy, anemia, heart conditions, age etc Dysthymic disorder, is a mild but chronic type of depression but its your ocular pain (left eye) and persistent degrading vision in the same eye that imho is a heads up to the potential of something like optic neuropathy or an ocular disorder especially retinal disease and may be the clue to working this out for you.