"Soul"

Time was an unknown concept inside the Chamber. It could be a day that has passed in reality, weeks, or months. But feeling his body weakened even though he rarely does nothing hinted to Ned that whatever happens outside the Chamber reacts to his body (or thought) inside the Chamber. 

He had been sitting in a cross-legged position for only half a minute (little less if he included all Master Wills lecture) but feeling his body waning, his hands shaking, and his vision blurring, Ned was reassured that he need not stay any longer inside the Chamber. 

"Agreed," Master Will said, none hinting any concern as he sucked smoke from his wooden pipe. "What's the point of all these if you're to die in reality."

Ned opened his other eye while raising an eyebrow. The 'Life training' as Master Will called it, had to be suspended for Ned to have the senses back to reality.