I Had An Episode Of Pounding Rapid Heartbeats, Dizzyness, Lightheaded,

I had an episode of pounding rapid heartbeats, dizzyness, lightheaded, chest tightness that lasted over 17 hours, then it stopped. I couldn't take my blood pressure because it wouldn't register normally on the BP kit. After 15 hours of this pounding and feeling dizzy I finally managed to get a reading on the BP monitor of 93/71 and P 120. After 17 hours it suddenly stopped and my BP was 115/73 with P 91. No swelling any where, but extremely weak and having difficulty breathing. Was this a life threatening episode? What was it? It has happened before but never lasted this long.