Anxiety can cause nervousness, fear, apprehension and worrying. One of the main causes of anxiety is the cumulative or long term role of stress, which if unmanaged, is known to lead to an increase in the likelihood of illness.
Most of our anxieties come from a fixation on the past of the present. When we meditate, we intentionally focus on the "here and now", which takes us out of the anxious mode. Meditating helps us to catch our breath and get perspective in order to feel calmer and more able to deal with situations that arise. It also helps to cultivate an attitude of non-judgmental acceptance.
In Mindful, Bob Stahl shares an article entitled "10 Mindful Attitudes that Decrease Anxiety" which you can access here.
The Mindfulness Project also has a range of great resources to help support your own practice, including videos, podcasts and helpful articles.