It is also one of the less common side effects of lithium.
More accurately, pupils that dialate and shrink visibly, for no apparent reason, and not synchronized with each other.
For instance in the episode of The Simpsons where Homer eats the Guatemalan Insanity Peppers. The scene where he looks down into the stream and can see his pupils going poppoppop! That's what I looked like.
It is very disconcerting to know that everyone around you thinks you are high as a kite, when you just need to take pills to keep from hurting other people...