Why is anaphylaxis a severe fear to people who had never experienced it from food and a common food allergy test was neg?!

Phobia: One can develop a phobia to anything -- and you've said in previous questions ; comments that this is the case with you. Phobias can range in intensity. The underlying (unconscious) process of "how" or "why" your mind creates a particular phobia depends on many things: your anxiety level, environmental influences, etc. Help is available with a good psychologist who can work with you. Best wishes.