You seem to be going through a tough time. It looks like you are talking of someone who stays with you through out the day and it scares you, other people can't see it hence can't understand or believe you.
Next Steps
Please see a psychiatrist and psychologist for full evaluation and diagnosis.
Health Tips
If it hasn't harmed you till now, probably it'll not harm you now. Ignore it if you can. Slowly it'll go away when you don't interact with it. Try to exercise regularly even though it's tough. This will help you to breathe deeper and your panic attack will reduce. Practice anulom vilom and bhramri pranayma every day thrice before meals for 5 mins each day. The more you practice this, the more your feelings of being threatened will reduce.