Firstly, the dipstick should only be "rested" on the crankcase hole where it screws in, in order to check the oil level

It sounds pretty terminal from what you say Val

As if you've lost all the oil somehow

And the crank has run dry and knocked the big ends out

Have you had an oil change recently ?
Is the sump plug still in the crankcase ?
Is there any sign of oil on the underside of the engine ?
I hope it's not what I think it is