What are the scenarios or reasons a nurse can lose their job or get fired? I’m worried as I’m always late because of exhaustion.

depends on where you work and what their policies are. If you live in an "@ will" state -they don't have to give a reason. If the hospital policy is such that they have to give you X number of written warnings - then you are warned and then fired

Try not to be late some supervisors do not appreciate their employees being late.
Nurses have been terminated for falsifying time, taking Tylenol, and not following policies and procedures.