Ni Dan,
Interesting observations. It could be many factors, but it seems that as long as you remain calm and in a calm environment, symptoms are not triggered. Maybe once you get in a more active environment, and then calm again, the unbalance is triggered. It could be related to cortisol levels, or adrenergic tone, going up that down, or even the bright outdoor light. You will have to make more observations, and try narrow down to the possible trigger.
About having a pupil larger than the other, that's a neurological symptoms. Do you have other neurological symptoms, like migraine, or double vision, or dropped eyelid ? This would tend to show that the oculomotor nerve on one side is affected by POIS, not unlike this can occur in a lateral migraine ( it is this nerve that control the dilatation and contraction of the iris, so the size of the pupil). It is maybe what is called in medical term an oculomotor nerve palsy, and not surprising, it can be caused by inflammation or auto-immune diseases (
https://en.wikipedia.org/wiki/Oculomotor_nerve_palsy#Acquired_oculomotor_palsy ). So, in my view, it is not surprising that it can be caused by POIS, because of brain inflammation, and, why not, third cranial nerve inflammation causing this nerve problem you mention. Do you have this symptom out of POIS ? If so, be sure to see a doctor about it, and rule out any other serious condition.
The timing could be hard to achieve, but it would be very interesting to see a doctor when while your pupil are of different size, so he could confirm what's going on. It is rare to have an easily visible, objective effect of a POIS attack.
