YABU (but only a bit) Why be scared? Most of the side effects are minor, and if they didn't tell you about the severe ones you'd be even more scared if you got them cos you wouldn't know what was wrong with you. And you wouldn't know that you might need medical help.
Sometimes some information is v helpful, though... Am thinking of how nice it would have been for the GP to mention that thrush is a common side effect of the anti biotic she prescribed and that it could (and did!!) impact my breastfeeding
Just about anything can have side effects - they only warning you of the worst case scenario - I have a MIl who does much the same about everything 'Don't walk to the park, a car might be driving along, lose control and run you over' 'Don't chew gum, you might tip back on your chair and accidently choke to death' Etc etc, terrible story for every possible tenuous situation.
Antibiotics are pretty safe - probably have an many side effects from an untreated infection.