 While the individual diver cannot predict exactly at what depth the onset of narcosis will occur on a given day , the first symptoms of narcosis for any given diver are often more predictable and personal . For example , one diver may have trouble with eye focus ( close accommodation for middle @-@ aged divers ) , another may experience feelings of euphoria , and another feelings of claustrophobia . Some divers report that they have hearing changes , and that the sound their exhaled bubbles make becomes different . Specialist training may help divers to identify these personal onset signs , which may then be used as a signal to ascend to avoid the narcosis , although severe narcosis may interfere with the judgement necessary to take preventive action . 
