Is David Blaine showing signs of losing his grip on reality? Have the impromptu barbecues and egg and sausage slinging finally got to him? Will he survive - mentally and physically?

These are some of the questions being posed as the US illusionist reached the half-way stage of his 44-day vigil locked in a glass box above the River Thames without food.

Medical experts have warned that his endurance stunt could end up causing major damage to his health.

He is already showing the effects of isolation and he may eventually suffer hallucinations, they claim.

They are also warning about potential kidney and heart failure.

Blaine himself, speaking through a microphone, has described how his culinary cravings for food have led him to fantasise about his favorite foods.

'I close my eyes and see these vivid images. It's like I'm really eating it"' he said.

The illusionist can now only manage to stand for 10 minutes each day. He is complaining of feeling "really dizzy' at times, heart palpitations, and freezing at night.

Blaine has been observed performing ritualistic behaviour. He spends up to six hours a day rubbing his hair and glass-tapping.

He is also said to be moving or folding the duvet at least 20 times a day.

While he battles to maintain his grip on reality, Londoners who have gathered in their thousands to see him are showing little mercy to the American magician.

Onlookers tried to keep him awake day and night by throwing missiles or making noise. Others have teased Blain by cooking food underneath him, or stripping off.

One man was charged with trying to cut Blaine's water supply, the only food he is ingesting.

Another man was charged with criminal damage for allegedly throwing pink paint at his Perspex box which is suspended from a crane near Tower Bridge.

Doctors monitoring his progress said the relentless disturbances have now significantly increased the overall risk to Blaine's health.

Dr. John Potter, an expert on the psychology of solitary confinement, said he had observed mood swings, ritualistic behaviors and sharp spells of depression.

He also believed Blaine was showing signs of creasing withdrawal.

Dr. Mike Stroud, an expert in nutrient deficiencies, is reported to have warned of serious consequences if Blaine's salt levels - said to be very low as temperatures in his boxes reaches 40C - continue to drop.

If the salt depletion worsens he said Blaine could suffer confusion, kidney failure and an inability to stand up without falling unconscious.

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%.

He also runs the risk of heart failure, experts said, due to disturbance to sleep patterns and the shocks from thrown objects smashing against the box.

Extra police have been drafted in, such is the fascination for people trying to disrupt Blaine's efforts to sleep though the long hours spent dangling in the air.

Metropolitan Police said the US magician could face a huge bill for the policing of the event when he eventually leaves his box.

Blaine's endurance test is being filmed for television shows on Britain's Channel 4 and Sky One.