Asthma

It is usually something that develops in childhood and many grow out of it but some do still suffer in adulthood. There is also adult-onset asthma but the triggers are sometimes different.
The asthma uk website is very good http://www.asthma.org.uk
The best way I can describe how it feels when I personally have an attack (I am 29 but been asthmatic since I was 9-ish), its like trying to breathe through a drinking straw if you hold your nose. If the attack goes untreated your whole chest/ribcage starts to ache and you feel dizzy and paniky.

Everyones triggers are different, mine is bad with pollen, dust, perfumes, dogs and cold weather

If I have missed anything let me know and I will do my best to answer

I became asthmatic late 20's. Had always suffered with allergies before that tho & it runs in my family.

Basically, an asthma attack is very scary and deadly. A lot of people who don't suffer underestimate it. The main symptom is wheezing and inability to take a breath. Not nice.