I'm thinking of quitting my nursing job.
Why would you quit your job?
I don't feel like I'm intelligent enough to be a nurse.
It's fine to change careers if you feel like your current career doesn't suit you, just make sure you give proper notice before you leave your job. Abruptly leaving your job can cause staffing issues, and may result in you getting a poor reference.
I'll think about it some more.
I'm glad that you are fully thinking this through.