First of all, keep in mind that I am unable to diagnose you because I am unable to examine you, this forum is for educational purposes.
The symptoms you describe are most consistent with migraine headaches. If he has never had these type headaches before, there are several things in his current condition that might have lead to them. First, after surgery, many people take regular (daily or more) narcotic or other pain medications. This can lead to rebound headaches in susceptible people. Second the stress of the surgery and the disruption of his sleeping routine, can also precipitate headaches in some people. Of course, the first thing you should do is make sure these are not symptomatic headaches (from a tumor, vascualr malformation, etc.). The CT scan is a decent first step, but you need a MRI of the brain with contrast. Second, you should stop taking pain medication more than 2 times per week, and start a headache preventative medication(such as elavil, topamx, nadolol, etc). This is not easy, and in difficult cases a steroid taper is helpful to ease the transition over to the prevenative medication. In severe cases, patients may require admission to the hospital for IV infusions of Magnesium, Depakote and DHE. Migraines in general "feel better" when lying still, in a dark place that is quiet. However the fact that your husbands headache improves with lying down could also suggest a CSF leak, although this would be very uncommon after a testicular surgery.
I hope this has been helpful.