Thought I would share this (potentially X rated) incident as I found it an interesting experience.
My period started yesterday which mean that I woke up this morning with the headache and tingly tongue I associate with a migraine - small amount of rizatriptan (now 1/8 of a wafer seems to be the dose I need) sorted that out but later on - just after lunch time - when I was sitting on the sofa watching some tv and working on the crossword with the boyfriend I found that there was a gap in the middle of my field of vision - that point that I tend to use as the focus point for reading - and reading the crossword etc was just impossible - checked it wasn't the glasses and also checked that it wasn't something in the eyes (was there regardless of which eye I tried focusing with). Although it isn't something I've actually had on that scale before - problems with focus are something that I experience with my migraines (and not something that the rizatriptan will correct). Anyway crossword not possible so we moved on to other activities (leave that to your imagination :).
Anyway, post activities the problem resolved itself ... never actually observed it quite so dramatically but I have noticed in the past that for me such activities can be a way of easing a migraine ... though I know that varies from individual to individual.