Pretty common, based on my own experience and that of most of my older women friends. It could be related to age and hormonal changes, and also have some connection with your anxiety disorder. There's this ironic link between unacknowledged anxiety or tension, and a palpitation or two, and increased tension, and more palpitations.
Many of the women I know got through this with the help of some meditative practice that involved breathing or mindfulness. Yoga or various breathing practices or even gardening can help. Everybody I know has lived through it and eventually had fewer episodes, so try not to let worry about it make it worse.
You may be years out from menopause, but you're in a long stage called perimenopause, and the hormones and metabolism do begin to change noticably. Take good care of yourself.
Blessings.