The religion of Islam does not command a worship to anybody which exceeds their capacity and which they cannot bear or perform. For example, a person who cannot stand performs his/her prayers in a sitting position. If an expert and religious doctor tells somebody that it would be harmful for him/her to fast, then s/he does not fast. S/he fasts when s/he is healthy or if s/he will never be able to fast, then s/he pays a ransom: (to feed a poor person). (Fasting) for a fixed number of days; but if any of you is ill or on a journey, the prescribed number (should be made up) from days later. For those who can do it (with hardship) is a ransom, the feeding of one that is indigent. But he that will give more of his own free-will―it is better for him, and it is better for you that ye fast, if ye only knew. (2:184) Therefore, although a Muslim is to perform his/her worships by all means, s/he is responsible for what s/he can perform from these worships. And you also perform your worships according to your state and to the advice of an expert doctor. However, Allah will question His slaves because of the obligatory worships which they did not perform without a valid excuse.