What Causes Popping Sound In Head?

Husband just called and said he doesn't feel "right", he is angry, and out of sorts. I worry only because he said this came after he experianced a "popping" sound in the head. This all happened before he had laser treatment yesterday for Tongue cancer. He gets shots for the pain because the pills were not working. He is 39, 5ft 10 and 320 lbs. He has had various serious health issues before. Should I be concerned??