I recommend sleeping in a reclined position, that is the head of bed elevated and knees propped up for about 2 weeks following abdominoplasty. After lying on your side for a while, the edema will tend to migrate to the side you are lying. Five days is a little early to sleep on your side.
If you are accustomed to sleeping on your side or your stomach, it can be very difficult to sleep on your back. Sleeping in a recliner at home may help. If that isn't possible, be sure to sleep with your head elevated on 3 to 4 pillows with your knees bent. You can rest your knees on 2 to 3 pillows. It may be too early to sleep on your side, but ultimately you should follow your surgeon's specific guidelines.