Himalayan ox is all right over going without oxygen (3)
I believe the answer is:
yak
'himalayan ox' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for yak that I've seen before include "one sporting a thick coat" , "Persistent talk" , "Hairy Tibetan ox" , "Long-haired ox of Tibet" , "Gossip; ox" .)