I've made a decision that I am probably going to postpone Sonic's vet visit that he is booked in for later today - his nasal congestion has eased a bit over the last couple of days, and his antibiotics related diarrhoea has cleared up. However, I don't think he is over his nasal issue enough to have his vaccinations, but it has cleared up a bit, and I think the stress of carting him up to the vet would be counter-productive today.
Don't get me wrong, if he had got worse or if anything serious seemed to be going on in the first place, I'd have him straight up there, but I think since it seems to be far from life-threatening and there has been some improvement, we would be better off just monitoring the situation for a few days. Trust me, I know everything that goes into my cats and everything that comes out of them, he is not seriously ill (a bit of nasal congestion and otherwise in good health, and the explosive bowel thing that was a side effect of the antibiotics is gone now) and I do not feel there is anything to be gained from a vet visit today - it would just be a "bring him back later in the week" visit.