Allergies are the result of a hypersensitive immune system. The allergic immune system misidentifies an otherwise innocuous substance as harmful, and then attacks the substance with a ferocity far greater than required.
Laying off an employee is different from firing an employee. Firing means letting a worker go for any reason, whereas a layoff refers to an employment termination based on economics, usually involving more than one worker.
In an economy based on at-will employment, such as that of the United States, a large proportion of workers may be laid off at some time in their life, and often for reasons unrelated to performance or ethics.