While reading a book on the signs of a sound heart I have come to find I am lacking in excitement, joy, and yearning for my prayers. If I try from now on to better this, what will become of my past errors ? Are all these past prayers lost opportunities ?

Ustadh AbdulAziz al-Haqqan

Your past prayers are valid and nothing is upon you for them, Imam Ibn Baz said they are all correct and what remains is only striving and asking Allah for tawfiq. What is diminished is the reward, not the prayer, so repeat nothing.