Just wondering about this symptom as I asked a medical secretary (not had a chance to ask a Dr yet) and she seemed to think it was rare for it to go on for more than 24 hours. I was due for an eye operation on Monday (cataract) and had to put one drop in before I got there. 2 hour round trip to the hospital, and then had 3 hourish wait having been told I was end of list, so not likely to get in the theatre until at least another 1.5 hours on top of this. I had 2 lots more of drops put in while waiting, and then at around 3.15ish it was suggested to me that I go home as they would not be able to fit me in that day! So.... very stressful, (and still no new date for the op) but the point about the post is that it took 3 days for the pupil to normalise to the size of the other one. That's today, and only just about there this morning, so that's over 3 days in fact. Is this an ME/CFS thing then? According to the net they say not more than 24 hours and that's for children.