Genuine Excuses For Not Fasting or Postponing

[1] Being sick
[2] A traveller
[3] Pregnant
[4] Breastfeeding
[5] Extreme weakness which can lead to illness
[6] Insanity
[7] Being unconscious for long periods, as in coma
[8] Striving for the cause of Allāh

When these excuses finish, one has to fast. If illness continues and the person is unable to make Qadhā at a later date, then they have to give fidyā, which is the amount of Sadaqatul Fitr for every missed fast.

Extracted from A Gift for Ramadhan, Page 49.

A Gift For Ramadhan – New 3rd Revised Edition