The best position to sleep with a pars defect is in a reclined position as if you were sitting in a recliner chair. If you have a recliner, you might even try sleeping in the chair for a few nights to see if it helps relieve the back pain from your pars defect. If not, you might use a stack of pillows to prop yourself up in bed. You might also place a pillow under your knees to further the relief. There are also adjustable beds where you can change your side to mimic the shape of a recliner whilst still sleeping next to your partner. So, if you find that it relieves your back pain to some extent, you might consider investing in one of these adjustable beds. Keep in mind that these are only general guidelines and everyone's body is different, therefore requiring different sleeping positions. Try out a few different options of pillows propping you up or placed underneath your knees to find your ultimate sleep spot.