What is the ruling regarding a sick person's physical posture during prayer?

Primary text

If a sick person is able to perform a certain posture (standing, sitting, bowing, prostrating, or gesturing) at the beginning of the prayer and then becomes unable to maintain it during the prayer, the person must transition to what they are able to do and continue the prayer from that point, building upon what has already been correctly performed. Similarly, if a person is able at the start and then becomes unable, the prayer must be completed according to the current state because the preceding portion was valid.