Whether a fear is irrational or not, doesn't make a difference. To the person being tormented, it's as real as the chair I'm sitting on. The dread, the panic, it wears on you. That's what's wrong with fear. I think of Philippians 4:7... my paraphrase:
"And the peace of God, which surpasses all comprehension or understanding shall guard your hearts and mind through Christ Jesus."
The peace that comes from Jesus Christ is beyond comprehension. I may have every reason to have peace or every reason not to have peace. It doesn't matter. He is the God of peace. And I can have that in every circumstance. ("Now may the Lord of peace Himself continually grant you peace in every circumstance..." 2 Thessalonians 3:16) When my children are sick, when my husband is unexplainably late, when I feel weird, when I think of weird things, it doesn't matter, I can have peace... peace that will guard my heart and mind.