Final answer:
The nurse should ensure the safety of the patient and prevent them from falling.
Step-by-step explanation:
When a patient ambulating in the hallway complains of severe dizziness and begins to fall, the nurse should take immediate action to prevent injury.
The first thing the nurse should do is ensure the safety of the patient. This can be done by quickly moving to the patient's side and providing support to prevent them from falling.
The nurse can also call for assistance from colleagues to help stabilize the patient and assess their condition.