A panic attack is a sudden fear of impending doom.
The sufferer may feel like the are away to faint, have a stroke or heart attack or may even feel they may die.
Heart palpitations, shortness of breath, feelings of suffocation.
Tingles.
Sudden need to go to the bathroom.
The need to flee wherever they are.
Crying (usually occurs afterwards)
Not knowing what to do/confusion
Sweating
light headedness
Feeling unreal or that you do not exist
Hot flushes/blotchy skin/loss of colour

Just sheer panic.

EDIT:
How many panic attacks are you suffering a day? Or do you feel like this all the time? is there something that starts it off, like a phobia? you may have a panic disorder/anxiety disorder/phobic disorder.

You will need to see your doctor so he can rule out any physical reasons why you feel this way, but most likely you are suffering from some sort of anxiety.
And see the doctor asap. these disorders only get worse and more deepset if ignored.

Panic attacks are intense periods of fear or feelings of doom developing over a very short time frame — up to 30 minutes — and associated with at least four of the following:

Sudden overwhelming fear
Palpitations
Sweating
Trembling
Shortness of breath
Sense of choking
Chest pain
Nausea
Dizziness
A feeling of being detached from the world (derealization)
Fear of dying
Numbness or tingling in the limbs or entire body
Chills or hot flushes

If there is no physical cause for these symptoms it is determined to be a panic atatck.

See your doctor as soon as you can. if you think you're having a panic attack and it's lasting a few days straight, something's definitely not right. Hopefully a doc can help you sort out what triggered it and you can prevent another one from happening in the future, or at least have medicine prescribed that can help you.

One symptom would be panicking.