Stress and Anxiety are part of our life. But, as we know, too much of either can diminish the quality of our life. Many symptoms of stress and anxiety are the same such as tension, irritability, inability to focus, headaches, high blood pressure and loss of sleep, but stress and anxiety have very different causes.
Stress is usually a response to an external cause.
Arguing with a friend may cause stress or an approaching charging bull, where the stress subsides once the situation has resolved itself.
Anxiety is my reaction to stress; its cause is internal.
Unlike stress, anxiety can persist even after the stressor has passed.
According to the USA based National Alliance on Mental Illness , "all anxiety disorders have one thing in common: persistent, excessive fear or worry in situations that are not threatening."
For example, "I am worried that I won't be able to pay my bills this month" could be a stress-related thought and based on reality. An anxious thought might be "I am worried that my wife secretly hates me and wants to leave me, and when she inevitably does that, I won't be able to manage". This is stress about my thoughts or imaginings.
The Anxiety and Depression Association of America  states the “difference between stress and anxiety is the stress is a reaction to a problem, and anxiety is a reaction to the stress.”
The UK's National Health Service  defines stress as "the feeling of being under too much mental or emotional pressure," while anxiety is "a feeling of unease, worry or fear."
National Institute of Health's U.S. National Library of Medicine  says, "Stress is caused by an existing stress-causing factor...[while] anxiety is stress that continues after the stressor is gone." So, stress can start anxiety.
Stress is generally a temporary experience, while anxiety is a sustained mental health issue.
Anxiety is one of the most common mental health issues  and is on a par with depression. It can develop into social anxiety, panic disorder, phobias, generalised anxiety, obsessive-compulsive disorder and post-traumatic stress disorder (PTSD). A panic attack (as distinct from just feeling a bit panicked) is a sign of anxiety not stress.
One symptom clearly signals anxiety and not stress: a persistent feeling of apprehension or dread. With stress you know what the problem is but with anxiety you are often less aware of what you are anxious about and where your reaction is the problem.
Anxiety also leads to “solutions” for anxiety such as alcohol use/abuse or other short term relieving long term exacerbating strategies.
Why does knowing the difference matter?
Knowing the difference between Stress and Anxiety is crucial to finding an effective treatment and feeling better.
Sustained anxiety needs to be treated as its own issue as it doesn’t resolve when the stressor is gone and a holiday while good for stress will likely not do anything for anxiety.
Stress can often be addressed in a fairly practical manner, for example through exercise; whereas anxiety may require professional psychological treatment, counselling, or medication.