I think fear of spiders, heights, etc... are pretty rational. Perhaps some biological hardwiring sending messages to stay away from things that would hurt/maim/kill us since we lack natural defenses.
I am afraid of one thing that I find to be irrational: MOTHS! I think it is the erratic beating of the wings coupled with how insane they are around light...literally sends me into a state of sheer panic.
"Everyone who believes in telekinesis, raise my hand."