Hi Simon
With all the usual caveats about medical advice on a bike forum
And not wanting to add to your understandable anxiety
But you might want to get your medical advisors to rule out MS (multiple sclerosis)
It goes under a number of other names these days, but pins-and-needles and numbness are prominent indicators for early onset of this condition
No doubt it will turn out – as usual for those of us of relatively advanced years – to be just another of those interesting temporary conditions our body turns up to remind us not to get cocky about our longevity, however fit we may feel.
Hoping for something utterly trivial!