Sayyiduna Imran bin Husain (may Allah be pleased with him) says: I was a man with many illnesses, so I asked the Messenger of Allah (peace and blessings be upon him) about performing prayer while sitting. He (peace and blessings be upon him) said: Your prayer performed sitting is half of that performed standing, and likewise, a man's prayer performed lying down is half of that performed sitting. That is, in terms of reward and merit.