It's normal, normal, normal!! When I hit 3-4 weeks post my TKR, I felt like i had narcolepsy. All I wanted to do was sleep. Your body's gone through major trauma and it needs rest so just go with it. Plus the opioids make you sleepy too. It may get worse before it gets better. Enjoy the naps, lay around in bed and just take advantage of it. You'll have plenty of time to get back to normal!