Depending on your age, you will become more sensative to certain foods. The basil may even have been old, or the dish may have been off too. Allergies do come and go though and most run a course of about 7 years. I can't stomach Rotten Ronnies (McDonald's) anywhere and I try to stay away from fried food as well. 'course those things are good to stop anytime.
Really all you can do is take an allergy test.