I think it may have been a combination of things. Several years ago, I had a similar experience in the shower. It was following a long work-out and I still do not understand the exact cause, but I imagine I was overheated and the hot shower did not help. In addition, suddenly getting up causes a severe fluctuation in people with generally low blood pressure. Thsi fluctation can lead to lightheadedness and even blacking out.
I found this forum because just yesterday I took a fall and severely injured my leg. I felt nauseous and momentarily lost my hearing. After speaking with my father, I learned that he has similar episodes and has even blacked out a couple of times when in severe pain. The last medical forum I wa son confirmed severe pain can indeed cause people to go into sock and I think in my case, I was starting to do just that. However, I didn't completely and it went away after just a minute.
I wouldn;t worry about it unless it happened again. You may want to consider doing one of the bloos pressue checks at the local drug store it you have them and see if your's is in the low range. If so, you can expect to have similar situations when rising to quickly.
It might be a migraine. There is a kind of migraine that happens without the head pain one usually associates with them, and they are definitely accompanied by limited vision. I can't remember if they are called "silent" migraines, but I'm sure you could google migraine and find the description. Since migraines often are associated with the menstrual cycle in women, that seems to make it an even stronger possibility.