Going without sleep, however, was a different matter.
Mae Chee Kaew passed most of the second month of her retreat in three postures: sitting, standing and walking, but never lying down. She started the “sitter’s practice” as another experiment, an attempt to find a practical way of accelerating her meditation that took advantage of her natural strengths. She discovered that refraining from sleep rendered her mind so bright and sharp, so calm and serene, mindful and alert, that she practiced continuously for twenty-one days without ever lying down.
With each day of sleeplessness, her meditation deepened and her confidence grew. Sharpened spiritual faculties made her courageous and daring, which coordinated perfectly with her bold and adventurous nature. Her unusual visions, more frequent than before, became more extraordinary as well: sometimes foreseeing future events or perceiving nonphysical realms; at times revealing profound truths of the Buddha’s teaching.
This reflection by Mae Chee Kaew is from the book, Mae Chee Kaew, (pdf) p. 85, translated into English by Bhikkhu Dick Sīlaratano.