I have a fear of breaking my neck. is this a common injury to happen to someone and does it take alot of force for it to happen or can it happen easy?

Takes force: If you don't have underlying medical conditions that affect your bones or joints it does take considerable force for it to happen (e.g. fall from a height, car accident/major trauma). Recommend discussion with a doctor licensed in your area. They can assess you and run tests to see if you have any medical disorder that increases your risk of fractures - or provide further assurance if you don't.

Phobia: Breaking ones neck is possible but not probable. That minute possibility snags our thoughts and feelings and makes us fearful. A phobia is an irrational fear and you may have one. Please see a clinical psychologist to help you deal w/this treatable situation. Peace and good health.

Depends: Really depends on what you do and how you protect yourself. There are high risk activities football, motorsports, that put you ask risk. Swimming not so much.