How much is too much worry?

How do I know if my anxiety is normal or not? I have always been a person who thinks a lot about things and it is rare that I don’t lie awake for a while most nights worrying about something or other. This is just always the way I have been, since I have been an adult anyway. A friend recently suggested that my worrying wasn’t normal and that I should consider seeing someone about it. It really surprised e to hear her say this as I had never really considered the possibility that I might be mentally ill. So is how I am normal or abnormal – and how can I tell the difference between the two?