Hi, you should go for complete thorough check up(Retina, rule out transient vision loss). Infact you should go for thorough Dry Eye check up also, which includes various test, that will tell the severity of dryness, in severe cases, lubricating drop won't be enough, other medication and lifestyle changes would be required to get rid of your problem.

Temporary darkness may be a sign of many disorders most commonly it is associated with migraine, ... Other causes can include various conditions which can be assessed only by direct examination. If the duration is less than 5 seconds then vascular causes are mostly the reason (although not exclusively). Sometimes it may be idiopathic also (which means without a discernible cause) Get a retina check up done.. In some cases a cardiac workup and lipid profile may be advised.. Do not worry till you actually meet the doctor...because the theoretical possibilities are many... Without one to one consultation it becomes difficult to pinpoint. Wishing you the best of health always.