I had no idea. No idea at all, that I would feel like a wrung-out wet lettuce afterwards and need a lie down in a darkened room 
DS (19) has had a fair amount of lessons already, and we went for a short practice drive earlier today. I've never been in a car with a learner before. He was reasonably ok for a rookie I suppose, but OMG the feeling that I wasn't in control of anything...
Please tell me that I will get used to it, and that it will get easier!!