You have not mentioned as to how and when your fear started. But the fact that you are having headache, negative thoughts and disturbed sleep suggest that you might be suffering from depression. The 'fear' you talk about could be the symptom of underlying depression.
Next Steps
You need to consult a psychiatrist, in person, at the earliest.
Health Tips
If you have been abusing alcohol, tobacco and any such stimulant/ depressive substances, I would advise you to immediately stop them, and inform the treating psychiatrist about your habits.