The Laws of Prayer /The Blessings of the Shema (71)

1. A person may recite the Shema standing sitting or walking. However, he should not recite it while lying either on his back or on his front, as he must not accept the yoke of the kingdom of heaven in an arrogant fashion, but he may recite while lying on his side. Ideally one should not recite it lying at all. (Shulchan Aruch and Mishne Berurah 61)

2. An ill person who finds it difficult to rise, may recite it lying down. He should turn towards his side. If he can turn completely on his side or he can sit, even if it is only for the first verse, he should do so. (ibid)