Almost everyone will be terminated at least once in their careers. Unless you work for yourself it will almost certainly happen to you. It may happen through acquisition, merger, downsizing or even by under-performance. The first reactions are typically dismay, anger and sometimes even relief.
The first question to address is whether or not you need legal counsel to assist you. If there is even a faint sign of discrimination of any kind (age, race, gender etc.) - hire a lawyer to review your situation and advise you in the process. Do not sign or agree to anything without representation by qualified legal counsel.
Most departures are negotiated. If you are the only person being let go, there is likely a wide margin in negotiating an appropriate severance package. If you are part of a large group, severance will most likely be tightly defined with little room to negotiate.
Career Transitions Workshop