this is consumptive fatigue (lao juan), a form of blood deficiency caused by injury to the source qi (yuan qi). when the source qi is deficient, the nutritive qi and blood in turn become deficient. the yin is then unable to contain the yang, which floats to the superficial aspects of the body.

the classic signs of ‘floating yang’ include a hot sensation in the muscles, a red face, irritability, and thirst with a preference for warm beverages.

the definitive (almost pathognomonic) sign is the flooding, large, and deficient pulse which reflects perfectly the weak yang qi dilating in an attempt to reach the superficial parts of the body. the pale tongue is indicative of blood deficiency.

the same pathological mechanism underlies the fever which follows a severe loss of blood. headache occurs in such cases because the process is relatively acute and therefore has some force behind it: when the yang floats to the head, it causes pain.

(bensky & barolet)