Ballet - excited and nervous

I don't go to the theatre as such, except taking the children to see the Christmas pantomime?- oh I did see 'Cats'.
My daughter has just phoned to say she is going to book us to see Swan Lake, as a xmas present. I don't know what to expect. I don't know what to wear. I have asthma and do have a tickly cough at the most inappropriate times. Help !