Simon wrote: "long cycle ride... low blood sugar... quite shakey"
I'm not trying to be a buttinski, but... if that's a hypoglycemia thing, it can be dangerous.
In my case, I always carry a source of fast-acting carbs with me at all times, even if I'm only going to the other end of the house. I might go days or weeks without any problems, but when my blood sugar does goes low (unpredictable), it comes on quick with little to no warning, and I have to do something to remedy it immediately.
I used to carry proper glucose tablets, which are designed to stabilize blood sugar in such instances. But since the pandemic began, every time I try to order them, they're out of stock (again or still). So I switched to carrying regular plain ol' white sugar packets (one teaspoon, 4 grams each) which at least I can buy locally. Takes about 4 packets (16g) to have an effect if I'm really low. It's probably the absolute worst and least-fit-for-purpose kind of sugar there is, but it's better than losing consciousness or worse.
Again, not trying to nag you, but I hope you carry something with you to bring your blood sugar back up if it gets too low.