Sleeping habits

Personally I don't have a abnormal sleeping habits..but, my oldest daughter does..she is 11 and since she was about 2 she would fall asleep laying down but before the night was over even a cpl of hours after she went to sleep she would be sitting up in the middle of her bed rocking...At first I thought something was wrong and she just sat up..But to find out she was sleeping..The Drs said it's because she has aslight problem sleeping on her back because she is having a hard time breathing thats why she sits up in her sleep...