how can you handle very high anxiety levels

my anxiety is so high often that little things make me nervous,i live in a 3rd floor apartment, so if i hear noises outside my apartment in the communal stairwell, i panic because i wonder who it is or who could be causing the noise............. same thing with mail or answering telephone calls....i have a fear of opening my mail for fear of what's inside? might it be worrying news.....and the same thing with phone calls...i worry who it could be phoning me and i panic and let it go onto the answer machine.

anyone got any advice for anxiety when it is that high and you're a nervous wreck?