It is not an offense if one is unable to worship due to sickness. It is an offense when an able person does not take any effort to recite the thaniyan.
For example, if one could not worship with their body, one can still chant vocally or mentally because the mind does not experience pain.
It is pertinent that one should worship either physically, mentally, or vocally.
Scriptures do not say that one must physically prostrate, but it is considered a defect if a healthy person fails to do so.