High Pressure Nervous Syndrome becomes a problem if there is no nitrogen in the mix for major times at depth (saturation). The slight nitrogen buffer adds safety. And yes, Helium requires offgassing just like Nitrogen. Helium comes out more than 2.5 times faster, but Helium is also absorbed that much faster.
If you are really interested, you could do a lot of diving and get into a trimix class after a couple hundred dives.
Cheers and safe diving
