I had my surgery a few weeks ago and have the same problem. I also have sleep apnea, but no machine. I was diagnosed with apnea right before my heart problem and since I did not have any symptoms, did not seek treatment. I did not need one to get a nights sleep. I've done better now that I can roll over and sleep on my stomach, but still wake up about 4 times a night and don't get more than 3 continuous hours, but I can go back to sleep. I find that music helps and the repetition of the rosary.
If your sleep apnea machine worked in the past, you may need some adjustments since your surgery. Also, narcotic pain killers can make sleep apnea worse, has your sleep doctor checked out your current meds? I too nap and it helps also.