Seeing objects move when staring at them for prolonged time is pretty normal. I remember we even did excercise in school (like third grade) when teacher told us to focus on one point and start at until we start having "visions" (not sure i am using the right word. She did it not trip us... just to make us calm down and not run around all the time).

Everbody seen some distortions.

If you can tell it's not so, and it's just quirk of your mind, there is really no need to run to psych each time such a thing happens. Everybody's mind can start act slightly strange or off when tired or stressed. As long as you can tell it's just a trick of your processing... you are fine.