for work law is emphysma classed as a disability

i have been off work for a prolaspse operation but also have had  emphysema for three years  after going to occpational health i recieved a copy of a letter to my employer stating she does not consider me to come under dda.
i have reduced my hours at work so i can maintain working as i do get alot of infections and grt tired and need to rest. i have been told that i am classed as disabled by my union rep
what is right?
i am worried my work will try to finish me on capability grounds    
i am already stressed as i am waiting to go back into hospital for more work on my bladder
sue

[National Jewish Health]

The best advice I can give you is for you to go to the source; the ADA Information line at  http://www.ada.gov/infoline.htm.   For general ADA information, answers to specific technical questions, free ADA materials, or information about filing a complaint. You can also call  800 - 514 - 0301 (voice), 800 - 514 - 0383 (TTY)

Good luck,