Peace Sister_J
Have you heard about the marathon monks? They go without food, drink and sleep for a long time.
I guess it is a matter of practice and self-discipline and part of that self-assurance comes from the belief that Allah (SWT) has power to sustain us.
This is not special to Sufis this is what we as Muslims believe. For those who deny the gifts that Allah (SWT) gives to the pious have not understood the fundamental ‘reality’ of this world. Allah (SWT) can grant anything He likes.