Erratic thumping in the region of the heart is a typical sign of thyroid trouble. Also a horrible thumping in the throat and a feeling of anxiety.I would call it palpitations. Dizziness too.Very scary.. Sweating ,thinning hair,dry skin, splitting nails, tiredness and weight gain.I am also post menopausal and it turned out to be an underactive thyroid.
Get yourself to your GP post haste where they will do tests.
Nothing to worry about if this is what you have .Easily controlled with medication . Hope you get it sorted and that you soon feel better.