Oh dear, I am fairly certain I have broken the Presta valve on my rear tire.
Narrative of events:
Contemplate extreme hunger, think about eating something, then realize if I do not do bike trainer ride now it's not happening.
Change into bike clothes, including socks.
Switch skewers, get bike into trainer.
Grab pump to get tire pressure up.
Belatedly realize I have not quite done something right (I still find those valves confusing in any case!) and that tire has now completely deflated.
Tinker with valve, on assumption that I am doing something wrong.
Think about how it is a bad idea to undertake a workout when already very underfueled-feeling, resist impulse to burst into tears at continued inability to fix problem!
Check out road bike repair manual.
(Resolve to take tires on and off at some near opportunity and get over bicycle maintenance fears. It always seems as though it will be impossible to put things back together, I do not have a strong urge to take things apart, could never have been a scientist!)
Examine valve on front wheel.
Reexamine valve on back wheel.
Check things on internet.
Conclude: I have broken the valve, though I should look again in the morning in daylight and when well-fed. BUT there is no reason to freak out. (Even if I have made a mistake and it is NOT broken, there is no shame in not really understanding bicycles.) I need to take it in to the store where I bought it for the brake cable check, I never did that soon after I first bought it but now I did that long ride it is a good time to take it in. And I will throw myself on their mercy re: this wretched valve.
Now I am going to eat something which will restore my mental capacities I hope...