David Blaine's endurance stunt is set to cause major damage to his health, medical experts have warned.
Blaine is complaining of feeling "dizzy"
The US illusionist has reached the half-way stage of his 44-day vigil locked in a glass box above the River Thames without food.
Dr John Potter, an expert in solitary confinement, said Blaine is already showing the effects of isolation and may eventually suffer hallucinations.
Experts are also warning about potential kidney and heart failure.
Blaine has chosen to be suspended by a crane by the River Thames - a stunt which has attracted thousands of onlookers to the site near Tower Bridge, many of whom are intent on disturbing him.
As well as trying to keep him awake day and night by throwing missiles or making noise, other onlookers have also teased the illusionist by cooking food underneath him, or stripping off.
One man has already been charged with attempting to cut Blaine's water supply, the only liquid or food he is ingesting, while another man was charged with criminal damage for allegedly throwing pink paint at the box.
Doctors monitoring Blaine's progress said the relentless disturbances have now significantly increased the overall risk to Blaine's health.
Dr Potter said that signs of the psychological effects brought on by isolation and lack of mental stimulation were already starting to show.
Blaine has been seen performing ritualistic behaviour, spending as
many as six hours a day rubbing his hair and glass-tapping, and placing
disproportionate focus on the positioning of his duvet inside the box.
He is said to be moving or folding the duvet at least 20 times a day.
And Dr Potter said he predicted that Blaine's experience would become increasingly unpleasant.
"David is increasingly showing signs of withdrawal, and this will increase as he focuses more on the internal world and leaves the external world behind," he said.
"Reported examples of hallucinations include imaginary changes to wall texture and the appearance of imaginary creatures and faces."
He is said to be folding his duvet up to 20 times a day
Blaine has also not been helped by recent high temperatures, which have caused him to lose salt through sweating at a much higher rate than expected.
The illusionist can now only manage to stand for 10 minutes each day.
Experts warned that if the salt depletion worsens it could cause problems such as confusion, kidney failure and an inability to stand up without falling unconscious.
And with the onset of colder autumn nights, Blaine may also suffer because when the body is starving its ability to heat itself declines by more than 50%, according to doctors.
Speaking into the microphone in his box, Blaine said: "I can still stand, but I feel really dizzy now.
His stunt lasts 44 days
"My heart beats really fast. It's freezing at night."
He also faces the risk of heart failure, experts said, due to disturbance to sleep patterns and the shocks from thrown objects smashing against the box.
An independent nutritionist is monitoring Blaine's urine to ensure that no "trickery" is allowed to take place.
Such has been the fascination for people trying to disrupt Blaine's efforts to sleep though the long hours spent dangling in the air that extra police have been drafted in.
But Metropolitan Police Commissioner Sir John Stevens said the US magician could find himself faced with a huge bill for the policing of the event when he eventually leaves his box.
Blaine's exploits are being filmed for TV shows on Channel 4 and Sky One.