Fasting is *typically* safe for *most people* but there are real potential risks and some people do have adverse reactions depending on conditions they may not even be aware of - or even *coincidental* medical problems that just happen to crop up at the same time someone is fasting. Fasting can do a lot of good in the right circumstances but its just not right to pretend that fasting cures everything and anything and that nothing can possibly go wrong (even if it might go wrong had someone not fasted at all). Any time someone is caughing up blood, there is something that should be investigated.