Why do I feel this? Shooting chest pain, profuse sweating, dizziness&lightheaded, paniky, hyperventilating, insomnia, worry 24/7, avoid places cause of fear.
Panic Disorder. It sounds like you are having panic attacks. See your physician for an exam and more details, and a diagnosis.
Need more info... This could be many things with just the above: thyroid, respiratory, anxiety/panic, prior traumatizing experience (s), etc. You should see a doctor (soon) for an examination, possibly some basic tests, and possibly referral to a counsellor and/or medication, depending on what the dr learns when talks with and examines you.
Panic disorder. You are probably suffering from severe panic disorder. You need thorough history, exam and proper treatment. This seems to be very disabling condition for you.