My husband was terrified of coasters at first, the trick is to start off slow! Especially not something that has inversions, those are worse. Just start with something slower/lower (I haven't been to SFGAm so I wouldn't know which) and build up from there, with sufficient time to recuperate. And celebrate for conquering it!
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Po!nt of View: A different look at Roller Coasters.
http://www.crosswinds.net/~justmayntz/thrills/index.html