It's like your Sunday school teacher used to tell you: if you have sex but are predisposed to rare eye conditions, you will go temporarily blind. Two UC Berkeley students with a medical blog looked into a rare case of post-coital blindness. Every time the unnamed patient had sex, he went temporarily blind afterward. The condition occurs when "the muscle walls contract around a blood vessel, restricting the flow of blood." Additionally, "Vasoconstriction is the same condition that causes erectile dysfunction." Really!
The study, originally published by the Department of Ophthalmology at Glostrup Hospital at the University of Copenhagen reports that:
The physiological response to sexual activity includes an increase in sympathetic nervous system activity, heart rate and systolic blood pressure. Our patient experienced transient monocular visual loss every time he reached the climax of sexual intercourse, but never while performing strenuous physical exercise. Hypothetical mechanisms of transient monocular visual loss in our patient include vasoconstriction or embolism in the arterial blood supply of the eye. The repeated and completely transient nature of our patient’s symptoms supports the fact that embolism was not involved, whereas the resolution of the symptoms after initiation of the treatment with the vasodilator enalapril supports vasoconstriction as the cause of transient blindness.
Try to unpack that. If you've never experienced it before, I wouldn't worry. Additionally, I wouldn't worry as it's only a temporary condition. Also, don't worry because it's the result of an orgasm, and that is cool.