You may get hypotension or anemia, if you can see some stars during taking a shower. When you take a shower, it will loss lots of energy which is caused by sugar. The hypoglycemia is sensetive to level of blood sugar, so you can see some stars. Insufficiency of blood supply and Oxygen reducing also can lead to such situation.
Your eyes may get the inflammation when you see some stars or spots when shower. The water may contain the invisible bacterium which may enter into your eyes. You'd better go to the hospital to have a full check on the eyes. Then you should use the eye drops to make the eyes get release.
There are many people who have asked this question. It may be floaters that haunt you. Floaters are dark specks in the form of dots, circles, lines or cobwebs that appear to move across the field of vision. The floaters move with the eyes, so you usually cannot focus on them. When you take a shower, your eyes are filled with water vapor, in this situation, your eyes will move all the time, and you will see some stars or spot in front of you. In general, floaters are harmless but if a large number develop suddenly or if they seem to be much worse over a period of time, you should seek medical attention.