Four stages according to physical ability

Prayer of the Sick: Standing, Gestures, Recovery and Unconsciousness

First: stand and perform actual bowing and prostration when able.

Second: if standing is impossible, sit but still perform actual bowing and prostration.

Third: if bowing and prostration are impossible, gesture with the head while sitting.

Fourth: if sitting too is impossible, lie down and gesture with the head.

One progresses to the next accommodation according to actual inability, not mere convenience.