Perhaps this information will help...

"Tryptophan may be high or low affecting melatonin and seritonin. Glutamine may be low leading to 'crazy thoughts'. Histidine may be low, leading to low histamine, which may lead to psychotic thought processes in some individuals."

Amalgam Illness: Diagnosis and Treatment by Dr. Andrew Cutler

Perhaps these irrational fears are related to these processes. I used to have them when I was a kid as well... terribly.