I'll try and answer this but, as I've never flown a fixed-wing thingy, there might some folk out there who could give you a better perspective.
Oh yes. You have to concentrate at all times. However, what you are concentrating on varies! I understand it is a lot harder on the whole to fly but, as you already have a PPL(A), you will be familiar with some aerodynamic characteristics, navigation and you'll be used to dealing with the radio. What you won't be used to is not taking your hands off the controls and having to memorize your read-backs to Air Traffic!
In the UK, you'll get 6 hours credit for having a PPL(A) but, be warned, very few people get through in the minimum hours.
Lastly, helicopters are not dangerous. Safety is paramount and that you will be taught. I've heard it argued that you are better off in a single-engined helicopter than single-engine aeroplane if the engine fails.
BUT....
Why helicopter pilots are different
Helicopters are different from aeroplanes.
An aeroplane, by its nature, wants to fly and. If not interfered with too strongly by unusual events or a deliberately incompetent pilot, it will fly.
A helicopter does not want to fly.
It is maintained in the air by a variety of forces and controls working in opposition to each other and, if there is any disturbance in this delicate balance, the helicopter stops flying; immediately and distrastrously.
This is why being a helicopter pilot is so different from being an aeroplane pilot and why, in generality, aeroplane pilots are open, clear-eyed, buoyant extroverts and helicopter pilots are brooding, introspective anticipators of trouble.
They know that if something bad has not happened, it is about to.
Cheers
Whirlygig