“What happens if you're allergic to anesthesia?”

Allergic reactions to some of the drugs used in general anesthesia are possible, but rare. Muscle relaxants and antibiotics are the most common causes. Allergic reactions to local anesthetics are usually caused by ester-type drugs, which are used much less frequently than the snide-type.

It is difficult to answer this, as there is no generic "allergy" to anesthesia, especially in a 28 y.o. patient. You may be allergic to some antibiotics, but you can get another type if necessary. You may have side effects from narcotics ( pain medication, usually nausea, vomiting or constipation), but you can get a different type of pain meds. But anesthesia per se (general, epidural, spinal, IV sedation) does not cause major allergic reactions.

Typically one is not allergic to anesthesia. You might be allergic to one or a few of the many drugs given during the course of an anesthetic, but there are so many options for anesthesia that most likely a safe and effective anesthetic can be administered if the patient is allergic to some drug given during a previous anesthetic.