Went round to see the Vicar’s Daughter.and promptly fainted 
Came round in a heap on the floor.
They helped me up and I was fine.
Worrying and baffling 
Yes worrying
Probably do not immediately tell your doctor, they tend to tell DVLA and then you can't drive until they're sure you're safe and that can take months - one of my mates hasn't been able to drive for nearly 6 months now. They stopped my brother driving for over a year for something they couldn't find.
Could easily just be dehydration.
Maybe take blood pressure and Oxygen level measurements - you can get the monotors cheap off Amazon