It would calm you to read what Professor Ashton, the author of the "Ashton Manual" writes abour palpitations:http://www.benzo.org.uk/manual/index.htm
"...Heart and lungs.
Palpitations, pounding heart, rapid pulse, flushing, sweating, and breathlessness are usual accompaniments of panic attacks, but may occur without panics. They do not signify heart or lung disease but are simply the expression of an overactive autonomic nervous system. Slow deep breathing and relaxation, as described under panic attacks, can do much to control these symptoms. Do not worry about them: they would be accepted as normal if you were running for a bus, and will do no more harm than if you really were!"
I find this very comforting to read. I find the palpitations hardest to deal with of the withdrawal symptoms, and I always get uneasy and even slightly panicky - I had an ultrsound of my heart resently and on the 21st IŽll have a MRI of the coronary arteries - and if that turns out well, then I have promised myself to believe the results!
Best of luck to you - and read the manual, if you have not done so already. Heather knows best