I am feeling better now that I am at home and resting. No, we just went into Sainsburys and sat for a while, and had some tea. I felt better after a bit, and was ok walking back to the bus stop and all the way home, although I still feel a bit "off." My sats sitting are ok, and all I plan to do this evening is sit. I will phone the GP very first thing in the morning and tell them what happened, and that I need to see someone (not necessarily the same GP, although I'd prefer that) ASAP. They don't do appointments on Tuesday afternoons, so I'm not sure how things will work out, but the Daughter will get me to wherever I need to go, if I need to go somewhere. If I feel unwell later this evening, I will phone 111.
As you say, something is definitely not right here.