The pain experienced during descent is the result of a pressurization change, and it's taking place in the sinus cavities. I've been hospitalized several times as a result of sinus blockages. In each case, I wasn't even aware I had a blocked sinus. It's seldom a problem when climbing; typically as the air in the sinus expands and cabin pressure drops, it vents out of the sinus easily enough. However, on the descent, it won't re-enter the sinus, and there's a low pressure in there.
If you've ever watched a water bottle on the ride down from altitude, you probably saw the water bottle slowly collapse and crush...the sinus cavity is experiencing something similiar. While the cavity itself doesn't collapse, it can do damage to the soft tissue lining of the sinus, which can separate, and cause an enormous amount of pain.
The rate at which the cabin pressure changes has a lot to do with it, but the overriding factor is the condition of the patient, in this case, your husband. A technique known as the "valsalva maneuver" is sometimes used to allevaite this condition, but it's not always successful. In a nut shell, one takes a deep breath and closes one's mouth, then pinches the nose while attempting to "blow." This pressuirzes the sinus cavities and may help inject some air, to alleviate the condition. Sometimes placing a warm, moist towel over the face can do it too...and back on the ground at home it's often helpful to take a warm shower and let the steam go to work.
A sinus blockage is one of the most painful things I've ever experienced, and had I not felt it first hand, I wouldn't have believed it. It can be completely debilitating. The first time I experienced it, I hear a bang and felt as though someone had smacked me in the head with a cricket bat. It really hurt. I ended up in the emergency room at the hospital twice as a result of that incident. On another occasion, also as a passenger, I was having headaches for a month, and was deaf for that month, too.
I didn't feel sick at the time, before the flights, but it's a good reminder to never fly sick...there's an increased possibility of ear blocks and sinus blocks if one is flying when sick. If it doesn't go away right away, visit a doctor.