Major Panic Attacks, Please Help!

Hello, I am a 23 year old male and I am terrified there is something wrong with my heart. About a week and a half ago I got back on Zoloft after a break for about a week (I ran out) I started at 25mg and have been increasing it by 25 every two days. I am now at 125 mg and plan to level off tomorrow at 150mg. Sense about two days before I started up the medication again, I have been having crippling panic attacks. My heart has always been a cause for concern for me (even though I have no history of heart or other medical problems besides anxiety) but the symptoms I have now with my attacks seem to be closer to actual heart symptoms. I always feel gassy or have the need to burp or cough, I often feel a lump in my throat and sometimes I get pains in my jaw. I have had minor palpitations for many years and payed them no mind, but these seem to set off attacks for me now, although I have read they are common with anxiety and/or Zoloft. Even with all this I very rarely experience any actual chest pain, at least that I can't tell is being caused by gas. The only exception was during the first of these major attacks, which was after a run and while my brother was talking me through the attack it felt like my chest seized up, but the pain left as quickly as it came in less than a second. I am young, fairly fit, and have excellent endurance, which I assume means my heart is healthy. I keep telling myself this is all just a really bad row of panic attacks, but I am terrified that there is actually something wrong. I have an appointment with my psychiatrist to discuss these symptoms on Monday, but I need to hold out until then or until the meds kick in. Can someone tell me if they experience any of these symptoms or confirm that at my age and lack of obesity I have nothing to worry about?