I first learned of Sadhu Haridas just this year while reading Man's Eternal Quest, an anthology of talks given by Paramhansa Yogananda (the first of three such anthologies put out by SRF, each, I assume, about 500 pages long. To be fair, I may have read something about him in passing in some other book and simply forgotten, though I don't think it is pertinent to this subject.). Yogananda mentions Sadhu Haridas performing a feat similar to that of Pilot Baba, namely, he was buried alive for forty days in 1837 with only the limited supply of air inside the coffin, and when he was dug up he sprung out without any ill effects.
An article written at the time by Claude Wade, describes the situation as follows. Sadhu Haridas, refered to as the fakir, was tied into a white linen bag "squatted like a Hindu idol" (lotus posture?), with his ears and nostrils plugged with cotton and wax. He was then sealed with a padlock in a wooden box measuring four feet by three feet and buried in a cell three feet beneath the ground that was just big enough for two men to sit inside next to the box (in another article the box is said to be four feet by eight feet, see Cpt. Osborn link below). This cell was dug inside a small room made of brick. The door was made of heavy wood sealed also with a padlock and mud (so people would know if the room had been opened before it was supposed to). The building belonged to Ranjit Singh, the Maharaja of the Punjab, who placed his personal seal on the door to prevent it from being tampered with. He placed four guards at the door who were relieved every two hours, day and night, for the duration of the forty days.
Mr. Wade describes the moment when Sadhu Haridas was removed from the wooden box:
"The servant then began pouring warm water over the figure; but as my object was to see if any fraudulent practices could be detected, I proposed to Runjeet Singh to tear open the bag, and have a perfect view of the body before any means of resuscitation were employed. I accordingly did so; and may here remark, that the bag, when first seen by us, looked mildewed, as if it had been buried some time. The legs and arms of the body were shrivelled and stiff, the face full, the head reclining on the shoulder like that of a corpse. I then called to the medical gentleman who was attending me to come down and inspect the body, which he did, but could discover no pulsation in the heart, the temples, or the arm. There was, however, a heat about the region of the brain, which no other part of the body exhibited."
Servants removed the stoppers from his nostrils and ears, bathed him in warm water, massaged his limbs, and gave him ghee to drink. After about thirty minutes Sadhu Haridas woke up and spoke to the Maharaja "do you believe me now?" to which the Maharaja "replied in the affirmative," and then bestowed upon the Sadhu a royal token reserved for princes and other persons of distinction.
Claude came out of the experience completely convinced that there had been "no fraud or collusion in the exhibition [they] had witnessed."
This event, according to a British Captain Osborn writing in 1880, was an experiment performed by the Maharaja who did not believe Sadhu Haridas could return to life from a deathlike state as he claimed he could. If we are to believe this account (and remember, vintage DOES NOT discount scientific experiments, otherwise every experiment ever conducted would have to be repeated every year because time erases factuality), then this provides a good example of the genuine scientific mindset alive and well in India more than a century ago. Just like the experiments with Prahlad Jani, genuine science can be performed to test yogic powers, NOT just debunking exercises. According to Cpt. Osborn, the Maharaja believed that fraud was involved and took every step necessary to prevent anyone from tampering with the Sadhu's body before the experiment was completed. The Maharaja was determined to leave the Sadhu's body inside the cell for forty days, and then discover either a living man, thus demonstrating his claim, or a corpse, demonstrating a fraud.
According to Cpt. Osborn, Sadhu Haridas lived off of milk for several days before being interred. On the day he was buried he swallowed thirty yards of linen and then brought it up again to clean his stomach. He then had his long beard shaved on the day he was buried in the ground and when he was dug up there was no hair growth on his face, which for the Captain proved he had been in suspended animation the whole time.
On the day he was buried Haridas first entered suspended animation; he "[layed] his tongue far back in his throat, crosses his hands on his breast, and suspends animation by means of holding his breath," and then was enclosed in the linen bag and locked into a wooden chest by the Maharaja himself. The chest was buried in a barley field and the above mentioned brick room was manufactured around where the chest was buried. (In the yogic tradition if one places the tongue up behind the palate they can stimulate a nerve that will allow them to go without food for several weeks or months. I've never met or read about anyone who has done this, so I can't say if it is true or not.)
What this experiment tells us, about yoga, or the siddhis, or human physiology, is, in itself, not much. No single experiment can stand as arbiter over anything. However, it does serve as one example among many that can lead us to certain conclusions, namely: 1. At least some siddhis are real (so far all those we can test have been demonstrated to be real), and 2. Human beings are capable of far greater control over their physiological functions than current medical science is willing to permit. In conclusion, I will borrow the words of Claude Wade on the subject:
"I shared entirely in the apparent incredulity of the fact of a man being buried alive and surviving the trial without food or drink for various periods of duration; but, however incompatible with our knowledge of physiology, in the absence of any visible proof to the contrary, I am bound to declare my belief in the facts which I have represented, however impossible their existence may appear to others."
The other wiki has a very short article on Sadhu Haridas that doesn't say much, if anything, beyond what is mentioned above.
Sai Baba's health is continuing to improve slowly after 15 days of hospitalisation. Updates can be found at this site created specifically for devotees to follow the progress of Swami's condition.