Please don't feel bad about not knowing these things. Lymphedema is breast cancer treatment's "dirty little secret," and few of us are told about it. Part of the reason is that our doctors and nurses aren't trained in it. A survey of U.S. medical schools two years ago by Dr. Stanley Rockson of Stanford University found that the average time spent teaching the lymph system in a student's entire medical school career is 15 minutes. (And no, that's not a typo!) Sigh!!
So we have to do a lot of educating of ourselves, and even of our healthcare professionals. Approaching them as partners can help, and providing them with evidence-based information. There's a page on the StepUp-SpeakOut website that you can copy off and give to your medical team here: http://www.stepup-speakout.org/what_we_need_healthcare_providers_to_know_about_lymphedema.htm
Wearing a sleeve for flying is somewhat controversial in the lymphedema community, because there has as yet been no careful, double-blind study done. All the evidence for compression sleeves and gloves helping to prevent lymphedema is anecdotal, but there's enough of it to make most therapists and lymphedema organizations suggest it. The National Lymphedema Network, for instance, has Position Papers on Air Travel, Exercise and Risk Reduction that suggest them for women at risk (which includes all bc patients). You can find the Position Papers here: http://www.lymphnet.org
There are two important guidelines for wearing garments if you have no symptoms (or even if you do!) They are: to make sure the garments are well-fitted by a lymphedema therapist or experienced fitter, and to wear a glove or gauntlet (fingerless glove) with the sleeve to prevent any swelling from becoming trapped in your hand. Here's a page about proper fit of garments, so you can judge for yourself: http://www.stepup-speakout.org/proper_fitting_of_lymphedema_garments.htm
If you decide not to wear garments to fly, consider getting them, trying them out to be sure they're a good fit, and at least bringing them with you in your carry-on baggage. That way, if you develop a problem on your trip you have a way to deal with it. It's no fun landing in some unknown city with a hand the size of a baseball mitt!
Willietats, yes, I really do believe every one of us should see a well-qualified lymphedema therapist for evaluation, preferably even before surgery. Baseline arm measurements are important for judging changes in circumference, and learning what to look for and how to reduce our risk is important for all of us. Also, a good therapist will be able to teach you a simple and gentle massage that you can use prophylactically to improve lymphatic function. If our surgeons had the training and the time to do this for us, that'd be fine. But they don't, so it's up to us to decide how proactive we want to be about preventing and dealing with this.
Hope that helps! Hugs all around,