You can study to become a 'Specialist Nurse' in whatever speciality you work in as a nurse, full time. So eg the ones who work in the Cardiac department full time, can apply to study for the Cardiac Specialist Nursing Degree. We happen to know a Mental Health Specialist Nurse, though we didn't actually meet him in the course of his work.
Because they do work full time every single day, with patients dealing with the specialism, they are complete realists and are extremely empathetic, they answer any questions and queries fully and kindly with the appreciation that the patient has a life and family of their own - and don't ever expect us to do more than we can, whilst still encouraging us. Very rarely critical. Years ago I'd happened to try something or another which entirely failed to have the desired effect - which when considered after the event it was actually pretty obvious it wouldn't work. So anyway, I told my DSN about this lash up and she said 'We-e-ell - that probably wasn't the best plan, was it?' - and then suggested what I might try instead, cos this other course would most likely achieve whatever it was I was attempting to achieve.
The nurse is there to help you! So accept the help, whatever help you need! If it's not as much help as you need - say so and ask for more!