It's unfortunately true that when you're an employee at will, they don't have to give you a reason for terminating your employment. However, the good news is that in most states, you're entitled to unemployment compensation if they fire you without 'good cause.' It sounds like they don't have good cause, or they would have been sure to tell you that so that you'd know you were not eligible for unemployment compensation. Hop down to your state office and get your paperwork going as soon as you can, Lost. Hang in there and take good care of yourself.