How many zertec allergy medicine would someone need to take for them to overdose and be sent to the hospital but not die?

Strange question. But I can tell you it is highly unlikely that you can kill yourself even with 20 x the recommended dose but you will likely feel miserable for awhile. If you are thinking about suicide, I urge you to call the suicide hotline now. Don't delay even a New York second.
Too much. Of any medicine is not good. Please if you are having these thoughts consult your doctor ASAP or call a depression hotline. I am concerned about your wellness. Zyrtec can make you drowsy. Do not take more than 10 mg at a time! If your allergies are still raging, try a nasal steroid. Never use Afrin; it is addictive. Good health. Be safe.