It's all bollocks - in the mind ....
That is, until you or someone close to you experiences it. My kids, thankfully, have grown out of it as far as I can tell, but the reaction, particularly my youngest, was amazing - for many types of fragrances and smells. A high like you wouldn't believe, she'd go absolutely ape - and stay there for a few hours at most. Then the crash, and inconsolable. Of course the people who triggered the high were often long gone by the time of the crash, hence my opening comment.
The biggest issue with sensitivity/allergy/whatever-you-want-to-call-it is the disbelief, denial and mocking from ignorant morons, both to your face and behind your back, and the constant wilful disregard by showing up with hair spray or perfume or whatever caked on like they were an undercover skunk.
Years ago when living in Melbourne we found a good doc - from memory Dr Colin Little in the Mt Waverley area?? (for all manner of allergies etc) He was 'unusual' to say the least, and it wouldn't surprise me if he's on the fringe of 'normal medicine' as judged by 'normal doctors' - but he was a godsend. He told us it was possible the kids would grow out of it, and thankfully he was right - but also said to remain vigilant and there were no guarantees. If you are in Melbourne, look this guy up, and be very careful not to be too quick to judge and I say that in a kind way.
One of the plus sides to dealing with fragrance allergies/reactions is discovering all the natural solutions to cleaning and fragranting (??) that you can use - often cheaper - and even the ones that smell (like vinegar and eucalyptus) often don't trigger the reactions that the chemical ones do (but not always, sometimes they do ... and I'm sure individual reactions will differ ...).