The disadvantages of going too far with this kind of spiritual investment, was that the person lost complete interest in material/corporeal existence and became fascinated with the concept of delving into himself as an objective aspect of nature only; something similar to what Gautama did when he realised his princely existence was not for him. In India such people are called yogis, because they use the extensive techniques of yoga to control all aspects of their physical, from breathing at undetectable rates, slowing down pulse rates to reach a sort of metabolic inertness to other less marvelous things like going without food or drink for prolonged periods. This is called sadhna or self realisation, (hence the term sadhu, also used for these ascetics), and these people were able to cut down their energy requirements to very low levels, so they could remain in a state of meditation for very prolonged periods. It would be fascinating to study one of them, I think, and assess the effects of such rigorous mental exercise on their faculties.