No, it's just a sign that you're going crazy.
haha, actually it depends on the type of hallucination you experienced. You say minor, but what does that mean exactly? Did you see some splotches of color morph into a figure, did you feel as though you saw something out of the corner of your eye, did you perceive movement when there was none....etc...etc.... Yes, I get minor hallucinations when I'm dead tired even when my eyes are open, it's normal, and I have no idea why it happens. I'm guessing your perception and reasoning centers are just not functioning at their optimal level.