An aristo have many poisons and burning token on him, and he also have on him side effects (from bachmann). this aristo need only 1 damage to go the infirmary. During the state phase : - we flip all the red side up tokens -then he take enough damage to go to the infirmary, but at the same time we have to remove the poison and burning state who showing their blue side. So in that case, this aristo will go to the infirmary without the poison and burning token ? (even if he had or not side effects on him)
Once flipped and dealt damage the burning and poisoned tokens are removed immediately. Here is the poisoned example: https://aristeiathegame.com/wiki/article/41-poisoned Remove the Poisoned State token immediately after showing its blue side. Side effects is interesting for any other state. Imagine dying being immobilized and coming from the Infirmary being immobilized again.
You must consider you are flipping all the State tokens at the same time. Not one by one. As @HarlequinOfDeath said, Side Effects is intended to work with States like Immobilized.