Can Intense Spiritual Practices Cause Disease?
Yes, intense spiritual practice can totally devastate the body. The incarnations also take upon themselves the ills of the world and of their devotees. This was mentioned by Bhagawan Ramana Maharshi, Sri Ramakrishna, and also Sri Aurobindo.
I do not remember exactly what Bhagawan Ramana said but Sri Ramakrishna pointed to a devotee who he had reformed from a great sinner to one of the greatest saints of his time. Sri Aurobindo said he had taken upon himself some force that would have harmed India.
Sri Ramakrishna suffered from throat cancer which began as a clergyman's sore throat. He refused to stop talking to his devotees which aggravated his illness. He prayed to Mother Kali to be cured but was rebuked in return. He then bore everything calmly though one incident did reveal publicly that he was above the ailment. (He rushed out of his deathbed to save some devotees from a poisonous snake. He chased the snake way and managed to sneak back to his room but someone saw him in the process).
Incidentally Sri Ramakrishna was cured of many an ailment by ayurveda. Ayurveda recognises such ailments as "yogaja vyadhi". He was also helped by homeopathy being treated by Dr Mahendra Nath Sircar himself. In the last year allopathy was tried but he refused to listen to any advice. His doctors were usually so enchanted by his words and personality that they neglected their practice to be by his side. They also marveled at his mental clarity and sense of humour even while suffering so much pain and anguish. One of them even examined his samadhi state by touching his eyeball and testing for signs of breathing. The eyeball did not move and there was no breath.
Bhagawan Ramana was operated upon his cancerous tumour without anaesthesia. He too thus proved that the illness was under his control. He had refused the operation but concerned devotees forced him into it. Earlier also Bhagawan had borne the bites of rats as he meditated in a deep crevice of a temple. A devotee of Sri Ramakrishna, Swami Turyiananda too underwent a major operation without anaesthesia.
Sri Aurobindo refused treatment at the end of his life (He was never in favour of allopathy and was a bitter critic of the science). His physician declared him dead and wanted to give orders for cremation. But The Mother said he was not really dead which made the doctor suspect the sanity of The Mother.
Then he witnessed the sight, aided by the yogic powers of The Mother, which he could not forget ever. A great beam of light alighted on the supposedly dead body of Sri Aurobindo and with great force too. After sometime the light receded, but even then The Mother waited for three days. During this time a clear and bright bluish light was seen as an aura around him. Those who have seen the photograph of that time will know. Those photographs have now been taken out of circulation. Only when the aura receded was the body buried.