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.
How long you are off work depends on your occupation. If you do clerical work (i.e. stockbroker, teacher, or programmer), you can return to work when you feel up to it. This usually takes about seven days. Do not go to work for three weeks if you do manual labor (i.e. entertainer, truck driver or personal trainer).