Originally Posted by Desert
If a person fears his sickness will increase or his cure will be delayed by using water, then only he may make Tayammum. This could be done in even though it be with the assistance of somebody.
Salaat may be performed lying down only if one is unable to even sit and read the Salaat. This is done by lying on your back and placing a pillow behind your head, thereby, facing towards the Qibla and raising the knee if possible. (Tahtaawi pg.234)
Note: Nobody, while being sick, is exempted from praying salah