Melody
Some restaurants use chemicals on the lettuce to keep it fresh longer. This is what alot of people have a reaction to. Also you didn't mention whether you used any salad dressing, MSG can cause a reaction like you described and could have been in the dressing or on croutons. I have a similar reaction to even a tiny bit of MSG and I have to carry an inhaler and fast dissolving antihistamine tablets with me at all times. I don't eat anything that is in question, it's just to scary. Good Luck!