Long term results
It seems to be subsiding.
I have substituted the 1/4 asprin for nuts. Hazel Nuts (actually filberts from USA) &/or almonds (shelled - from the cooking shelves of the supermarket) and it is now managable.

The general feel - having listened to my body - is gut flora may be implicated (or a result of the same unspecified cause). Certainly things I hadn't noticed gone - are back in the diurnal rhythms.

If I do wake-up and feel the problem is threatening (in a mild way) I just expose a limb to cool the situation. I doubt the bedclothes are too much. One fairly slim duvet and no heating from about 10pm and the thermostat is set around 15 degC anyway.

Anyway thanks for all the ideas.