Congrats on the new position! I just made a similar move to the NICU after 5 years in adult world - last 3 being in the neurosurgical ICU. I absolutely love it so far and don't regret changing specialties. However like you, I'm unsure of exactly what I'd like to pursue in the future and worked so hard for (and am proud of) the skills that I gained as an adult critical care nurse that I wanted to continue picking up per diem shifts in neuro. Unfortunately, because I am working full time in the NICU of the same hospital as my old unit, I'm not allowed to technically be per diem on my old unit. Luckily, there is a loophole that allows me to pick up overtime shifts in neuro when they are short staffed so I have been trying to take advantage of that when I can. And I gotta say, those OT shifts have surprisingly been a welcome "break" and easy money. I know how things flow in neuro, I was a charge nurse and a preceptor and generally had a good handle on most situations that were thrown at me. If I don't know the answer, I know how to escalate to someone who does or who can help figure it out.
After almost 6 months in the NICU, although I love it, I'm not comfortable yet. There is so much to learn (or unlearn and relearn from the adult world) and the expectation as a newbie on the unit is to take the most critical or admission assignments every night. I'm not complaining, it's been a great learning experience but sometimes you just want to not have to think so hard!! Lol
Sorry for the novel, but I'd say if you have the opportunity to stay per diem in your old unit, I would take advantage of it while your adult skills are still fresh and you are figuring out what your future goals are. If you decide down the line that it's too much while orienting to a completely new specialty or don't feel like you will pursue anything in the future that would require it, you can always quit.
I was nervous going back for the first time after a couple months away from adults, but it was like my autopilot clicked and I got RIGHT back into the swing of things. Plus my BS tolerance is significantly higher now that I don't have to deal with the BS on a full time basis