How to get a full night's rest with cat allergies as houseguest?

Benadryl (diphenhydramine) Dr. Cordas' great advice may be difficult to perform when visiting the home of a cat owner. Let your host know about your problem. Keep your bedroom door closed to exclude the cat. Keep the window open to bring in fresh air. Take Diphenhydramine (benadryl) before retiring. In addition to being a good antihistamine it will also make you sleepy - an added benefit in this particular situation.
Cats. The dander from the cat is the main culprit, though the urine, saliva, feces, and even vomit can be allergenic. Don't let the cat near your bedroom. If the cat was on your bed in the past, vacuum the matress, boil the sheets, dry clean the covers, vacuum the carpet. You may have to do this several times to get rid of the dander. Using salione or steroid sprays at nite might help.