It is compulsory for a sick person to observe his salat according to his capabilities. If he is able to observe it like the healthy people, then he must do so, but if he is not capable, then (he observes it) according to his strength.

The sick person has to pray standing if he has the ability to do so. If he cannot pray standing, he can pray sitting, and if he cannot pray sitting, he should pray lying on his side with his face directed towards the Qiblah. If he cannot pray on his side, then on his back with his feet directed towards the Qiblah if this is possible, otherwise he can pray as his condition permits. Evidence of the above is the statement of Allah: “So keep your duty to Allah and fear Him as much as you can.” (At-taghabun: 16).


https://www.youtube.com/watch?v=Gd9eSK1q5EU