Had a panic attack that lasted 3 months. felt like i was suffocating for three months. would like to know how common this is.

Well, Most panic : Attacks reach their crescendo within 10 minutes ; then are on their way to resolution. Have you been formally diagnosed with panic disorder? You may have an anxiety disorder or another medical problem - but a single panic attack would not last for 3 months. So in answer to your question - never. Please seek medical evaluation for accurate diagnosis ; treatment.