The one thing I'd like to mention is that even though while you may be exposed to light 24 hours a day, you have eyelids and you sleep. Therefore you are able to escape from the light for the period of time that you sleep, and while you fall asleep your subconscious will probably send signals to pull your sheets over your eyes to block the light. You will not realize you are doing it, you probably will never know, but you're doing it anyway. No matter what your phobia is, your brain will do all it can to protect your body and it definitely does not stop just because you're sleeping.
Fish, like already mentioned before me, have no eyelids and they must rely on their instincts to find shelter....however, their brains do not work subconsciously like yours will and they can't exactly move while they're sleeping.
It's excellent that you care about your fish so much though!
Good luck ♥