I have an irrational fear of steep dropoffs, although more like excess caution and respect than fear per se. Well, the respect for them and the potentially crumbly edges is healthy, but the longer the dropoff the greater my respect. This is irrational since a 100' fall onto rocks below will kill me just as much as a 1000' fall. They both deserve the same amount of respect.
Other than that I sympathize with the OP... acrophobia would make it very difficult to be a cyclist in the SF Bay Area.
View from road up Mt Tamalpais