Anxiety:

Anxiety has been described for many years as excessive worry and nervousness that can be difficult to control or stop. Sometimes it's hard to keep fears and worries from interfering with one's daily life. Often times individuals will ruminate (think deeply) over everyday circumstances of which they feel they do not have the ability to cope with them.

I have found a major element of anxiety is Apprehension - the anticipation/fear that something unpleasant might happen. (Notice this is future oriented) A fear that something unpleasant might happen in the future. This apprehension causes a state of anxiety, which may cause one to feel:

When you are anxious your thoughts are likely to include:

"What if statement..."

Future Predictions

Panic Attack:

Uncontrolled anxiety can lead to Panic Attacks:

Panic attack is a period of intense anxiety that is characterized by fear and distress that is accompanied by various physical symptoms. Panic attacks can range from mild to severe in intensity, frequency and duration. The physical symptoms follow fearful or unpleasant thoughts, which can escalate rather quickly and cause discomfort.

Physical symptoms of a panic attack include feelings of anxiety plus:

When a panic attack is intense the person feels that they will not be able to cope with it and they must leave wherever they are at and immediately go home where they believe they will be safe.

Often times people mistake an intense panic attack as a possible heart attack and take themselves to the emergency room, only to find out it is anxiety.

Other times people do not realize they are having a panic attack because it is not severe and they did not "freak out".

Remember symptoms can range in terms of:

Intensity:      How severe the symptoms are. They can range from Mild to Severe
Frequency:  How often one experiences the symptoms or panic attacks.
Duration:      How long do the symptoms or panic attacks last for.